To see the other types of publications on this topic, follow the link: Contraction.
Journal articles on the topic 'Contraction'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Contraction.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Hogan, Michael C., Erica Ingham, and S. Sadi Kurdak. "Contraction duration affects metabolic energy cost and fatigue in skeletal muscle." American Journal of Physiology-Endocrinology and Metabolism 274, no. 3 (March 1, 1998): E397—E402. http://dx.doi.org/10.1152/ajpendo.1998.274.3.e397.
Full textAbstract:
It has been suggested that during a skeletal muscle contraction the metabolic energy cost at the onset may be greater than the energy cost related to holding steady-state force. The purpose of the present study was to investigate the effect of contraction duration on the metabolic energy cost and fatigue process in fully perfused contracting muscle in situ. Canine gastrocnemius muscle ( n = 6) was isolated, and two contractile periods (3 min of isometric, tetanic contractions with 45-min rest between) were conducted by each muscle in a balanced order design. The two contractile periods had stimulation patterns that resulted in a 1:3 contraction-to-rest ratio, with the difference in the two contractile periods being in the duration of each contraction: short duration 0.25-s stimulation/0.75-s rest vs. long duration 1-s stimulation/3-s rest. These stimulation patterns resulted in the same total time of stimulation, number of stimulation pulses, and total time in contraction for each 3-min period. Muscle O2 uptake, the fall in developed force (fatigue), the O2 cost of developed force, and the estimated total energy cost (ATP utilization) of developed force were significantly greater ( P < 0.05) with contractions of short duration. Lactate efflux from the working muscle and muscle lactate concentration were significantly greater with contractions of short duration, such that the calculated energy derived from glycolysis was three times greater in this condition. These results demonstrate that contraction duration can significantly affect both the aerobic and anaerobic metabolic energy cost and fatigue in contracting muscle. In addition, it is likely that the greater rate of fatigue with more rapid contractions was a result of elevated glycolytic production of lactic acid.
2
Conley, Kevin E., and Stan L. Lindstedt. "Energy-saving mechanisms in muscle: the minimization strategy." Journal of Experimental Biology 205, no. 15 (August 1, 2002): 2175–81. http://dx.doi.org/10.1242/jeb.205.15.2175.
Full textAbstract:
SUMMARYMany mechanisms reduce the cost of muscle activity. Here, we describe a set of specializations that reduce the cost of contraction in the high-frequency twitches that are used by a wide variety of animals for either sound production or flight. Minimizing the cost of these contractions means that cellular ATP production can meet ATP demand and sustain the high contractile rate. Two classes of specialization are found that minimize the contractile cost. The first class reduces the muscle work required per contraction. Light appendages such as rattles, insect limbs and membranous wings that require little work for movement are used in high-frequency contractions. The second set of specializations involves processes that minimize energy use. High-frequency muscles tend to have a lower cross-bridge content, fewer attached cross-bridges and shorter length changes per contraction. The result is low muscle-specific forces (stress), small length changes (strain) and rapid contraction times that suggest that these muscles push the lower limit of contractile function. The consequence of function at this lower extreme of contraction is to minimize the contractile cost of high-frequency muscles. Thus, specializations that permit rapid contractions at a low rate of ATP use per twitch are the basis of a minimization strategy for energy saving in muscles contracting at high frequency.
3
Hogan, Michael C., Bruno Grassi, Michele Samaja, Creed M. Stary, and L. B. Gladden. "Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow." Journal of Applied Physiology 95, no. 3 (September 2003): 1139–44. http://dx.doi.org/10.1152/japplphysiol.00226.2003.
Full textAbstract:
The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine gastrocnemius muscle ( n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O2 uptake, tension-time integral, and mean venous blood flow increased significantly ( P < 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 ± 6, 139 ± 8, and 145 ± 8 ml·100 g-1·min-1) and noncontractile phases (64 ± 3, 78 ± 4, and 91 ± 5 ml·100 g-1·min-1) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 ± 0.03, 0.32 ± 0.02, and 0.36 ± 0.03 ml·N-1·min-1, respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 ± 4, 30 ± 4, and 38 ± 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction.
4
Zuo, Li, Leonardo Nogueira, and Michael C. Hogan. "Reactive oxygen species formation during tetanic contractions in single isolated Xenopus myofibers." Journal of Applied Physiology 111, no. 3 (September 2011): 898–904. http://dx.doi.org/10.1152/japplphysiol.00398.2011.
Full textAbstract:
Contracting skeletal muscle produces reactive oxygen species (ROS) that have been shown to affect muscle function and adaptation. However, real-time measurement of ROS in contracting myofibers has proven to be difficult. We used amphibian ( Xenopus laevis) muscle to test the hypothesis that ROS are formed during contractile activity in isolated single skeletal muscle fibers and that this contraction-induced ROS formation affects fatigue development. Single myofibers were loaded with 5 μM dihydrofluorescein-DA (Hfluor-DA), a fluorescent probe that reacts with ROS and results in the formation of fluorescein (Fluor) to precisely monitor ROS generation within single myofibers in real time using confocal miscroscopy. Three identical periods of maximal tetanic contractions (1 contraction/3 s for 2 min, separated by 60 min of rest) were conducted by each myofiber ( n = 6) at 20°C. Ebselen (an antioxidant) was present in the perfusate (10 μM) during the second contractile period. Force was reduced by ∼30% during each of the three contraction periods, with no significant difference in fatigue development among the three periods. The Fluor signal, indicative of ROS generation, increased significantly above baseline in both the first (42 ± 14%) and third periods (39 ± 10%), with no significant difference in the increase in fluorescence between the first and third periods. There was no increase of Fluor in the presence of ebselen during the second contractile period. These results demonstrated that, in isolated intact Xenopus myofibers, 1) ROS can be measured in real time during tetanic contractions, 2) contractile activity induced a significant increase above resting levels of ROS production, and 3) ebselen treatment reduced ROS generation to baseline levels but had no effect on myofiber contractility and fatigue development.
5
Hamann, Jason J., Heidi A. Kluess, John B. Buckwalter, and Philip S. Clifford. "Blood flow response to muscle contractions is more closely related to metabolic rate than contractile work." Journal of Applied Physiology 98, no. 6 (June 2005): 2096–100. http://dx.doi.org/10.1152/japplphysiol.00400.2004.
Full textAbstract:
The magnitude of the blood flow response to exercise has been linked to both the contractile work performed and the metabolic cost of the activity. Under certain conditions, contractile work and metabolic cost may be dissociated. This study examined the blood flow response to trains of contractions when contraction duration was manipulated under conditions of similar tension-time indexes (isometric analog of work). Previous investigations have shown that trains of short-duration contractions have a greater ATP utilization, which may result from an augmented ion transport required for muscle activation and relaxation. On the basis of these findings, we hypothesized that the blood flow response would be greater to a train of short-duration contractions than a train of long-duration contractions. Canine gastrocnemius-plantaris muscle ( n = 8) was isolated, and blood flow assessed with an ultrasound flow probe placed around the popliteal artery. The sciatic nerve was stimulated to produce two contraction protocols that resulted in similar contraction-to-rest ratios: short duration: 0.25 s/0.75 s vs. long duration: 1 s /3 s. In accord with the design of the experiment, the tension-time indexes were identical for the two contraction protocols (short: 18.6 ± 1.0 vs. long: 18.6 ± 1.0 kN·s). Steady-state oxygen consumption was greater in the short-duration contractions (17.2 ± 0.9 ml·100 g−1·min−1) than in the long-duration contractions (11.7 ± 0.7 ml·100 g−1·min−1). Similarly, the steady-state blood flow was greater in contractions of short duration (125 ± 7 ml/min) compared with long-duration contractions (92 ± 7 ml/min). Contractions of short duration resulted in significantly higher oxygen consumptions and blood flows compared with contractions of long duration despite the same total contractile work. The blood flow response to muscle contraction appears to be more closely associated with muscle metabolism than contractile work performed.
6
Meisner, Joshua K., Randolph H. Stewart, Glen A. Laine, and Christopher M. Quick. "Lymphatic vessels transition to state of summation above a critical contraction frequency." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 293, no. 1 (July 2007): R200—R208. http://dx.doi.org/10.1152/ajpregu.00468.2006.
Full textAbstract:
Although behavior of lymphatic vessels is analogous to that of ventricles, which completely relax between contractions, and blood vessels, which maintain a tonic constriction, the mixture of contractile properties can yield behavior unique to lymphatic vessels. In particular, because of their limited refractory period and slow rate of relaxation, lymphatic vessels lack the contractile properties that minimize summation in ventricles. We, therefore, hypothesized that lymphatic vessels transition to a state of summation when lymphatic vessel contraction frequency exceeds a critical value. We used an isovolumic, controlled-flow preparation to compare the time required for full relaxation with the time available to relax during diastole. We measured transmural pressure and diameter on segments of spontaneously contracting bovine mesenteric lymphatic vessels during 10 isovolumic volume steps. We found that beat-to-beat period (frequency−1) decreased with increases in diameter and that total contraction time was constant or slightly increased with diameter. We further found that the convergence of beat-to-beat period and contraction cycle duration predicted a critical transition value, beyond which the vessel does not have time to fully relax. This incomplete relaxation and resulting mechanical summation significantly increase active tension in diastole. Because this transition occurs within a physiological range, contraction summation may represent a fundamental feature of lymphatic vessel function.
7
Kavvampalli Jyothirmayi Rani. "Some Applications via Coupled Fixed Point Theorems for (????, ????)-H-Contraction Mappings in Partial b- Metric Spaces." Communications on Applied Nonlinear Analysis 31, no. 5s (July 18, 2024): 351–71. http://dx.doi.org/10.52783/cana.v31.1055.
Full textAbstract:
This work establishes unique common coupled fixed point theorems for given mapping in complete partial b-metric spaces with the concept of (α, ϕ)-H-contraction in the context of partial b-metric spaces. (α, ϕ)-H-contraction Furthermore, we show how the results may be used and present applications to integral equations and Homotopy theory. Introduction In previous work, authors have discussed various fixed point theorems on partial b-metric spaces with (ψ, ϕ)-weakly contractive mappings, α−ψ-contractive type, Suzuki type contractions, rational contraction and H-weak contractions. In our work, with the help of (α, ϕ)-H-contraction, we investigated coupled fixed point theorems in partial b-metric spaces. Objectives: Finding the unique common fixed points for a given mapping in partial b-metric spaces via (α, ϕ)-H-contraction Methods with the help of α-admissible mapping, H-rational type, (α, ϕ)−H-contraction we have shown coupled fixed point findings in complete partial b-metric spaces Results: We obtained unique common coupled fixed point results via (α, ϕ)−H-contraction type for the given mapping in complete partial b-metric spaces. Conclusions: This present study uses contractive mappings of the H type in the reference of partial b-metric space to give some fixed point results, appropriate examples that illustrate the main findings, In addition, boundary value problems and homotopy applications are given.
8
Siegle, M. L., and H. J. Ehrlein. "Interdigestive contractile patterns of the ileum in dogs." American Journal of Physiology-Gastrointestinal and Liver Physiology 253, no. 4 (October 1, 1987): G452—G460. http://dx.doi.org/10.1152/ajpgi.1987.253.4.g452.
Full textAbstract:
The aim of this study is to elucidate the nature of ileal interdigestive contractile patterns by the computerized analysis of the contraction spread and by videofluoroscopy. Conscious dogs equipped with closely spaced strain-gauge force transducers were used. Two patterns of repetitive, phasic contractions were recorded, migrating clusters and phase IIIs; both patterns consisted of repetitive, propagated contractions. Both patterns migrated aborad by sequential movement of contraction waves down the bowel. Consequently, the rate of migration of either of the entire patterns was slower than the propagation velocity of constituent, individual contraction waves. Both patterns differed in several parameters, especially the propagated contractions of the clusters spread over shorter distances (1.47 +/- 0.4 cm) than those of phase III (4.65 +/- 0.99 cm). Compared with these complex patterns, propagating power contractions represented single contractions that propagated aborad at the same velocity as the contraction waves of the complex patterns. All three patterns propelled luminal contents distally.
9
Mehta, D., M. F. Wu, and S. J. Gunst. "Role of contractile protein activation in the length-dependent modulation of tracheal smooth muscle force." American Journal of Physiology-Cell Physiology 270, no. 1 (January 1, 1996): C243—C252. http://dx.doi.org/10.1152/ajpcell.1996.270.1.c243.
Full textAbstract:
The active isometric force developed by a muscle decreases at muscle lengths below an optimal length (Lo). However, when the length of an actively contracting muscle is abruptly decreased, a lower level of isometric force is reached during force redevelopment than when the contraction is initiated at the shorter length. This has been attributed to a deactivation of contractile proteins caused by shortening. In this study, intracellular Ca2+ and myosin light chain (MLC) phosphorylation were measured to assess the mechanisms for the modulation of isometric force caused by changing smooth muscle length before or during isometric contraction. The decline in isometric force between Lo and 0.5Lo was associated with decreases in MLC phosphorylation and intracellular Ca2+ during contractions elicited by acetylcholine or 60 mM KCl. Quick release of the muscle during contraction depressed force redevelopment at the shorter length but not MLC phosphorylation. We conclude that decreases in Ca(2+)-calmodulin-dependent MLC phosphorylation contribute significantly to the decline in isometric force at lengths below Lo, but the depression of contractility associated with the quick release of actively contracted smooth muscle is not caused by a shortening-induced deactivation of contractile proteins.
10
Todd, Gabrielle, Janet L. Taylor, Jane E. Butler, Peter G. Martin, Robert B. Gorman, and Simon C. Gandevia. "Use of motor cortex stimulation to measure simultaneously the changes in dynamic muscle properties and voluntary activation in human muscles." Journal of Applied Physiology 102, no. 5 (May 2007): 1756–66. http://dx.doi.org/10.1152/japplphysiol.00962.2006.
Full textAbstract:
Force responses to transcranial magnetic stimulation of motor cortex (TMS) during exercise provide information about voluntary activation and contractile properties of the muscle. Here, TMS-generated twitches and muscle relaxation during the TMS-evoked silent period were measured in fresh, heated, and fatigued muscle. Subjects performed isometric contractions of elbow flexors in two studies. Torque and EMG were recorded from elbow flexor and extensor muscles. One study ( n = 6) measured muscle contraction times and relaxation rates during brief maximal and submaximal contractions in fresh and fatigued muscle. Another study ( n = 7) aimed to 1) assess the reproducibility of muscle contractile properties during brief voluntary contractions in fresh muscle, 2) validate the technique for contractile properties in passively heated muscle, and 3) apply the technique to study contractile properties during sustained maximal voluntary contractions. In both studies, muscle contractile properties during voluntary contractions were compared with the resting twitch evoked by motor nerve stimulation. Measurement of muscle contractile properties during voluntary contractions is reproducible in fresh muscle and reveals faster and slower muscle relaxation rates in heated and fatigued muscle, respectively. The technique is more sensitive to altered muscle state than the traditional motor nerve resting twitch. Use of TMS during sustained maximal contractions reveals slowing of muscle contraction and relaxation with different time courses and a decline in voluntary activation. Voluntary output from the motor cortex becomes insufficient to maintain complete activation of muscle, although slowing of muscle contraction and relaxation indicates that lower motor unit firing rates are required for fusion of force.
11
Szarek, J. L., and N. L. Schmidt. "Hydrogen peroxide-induced potentiation of contractile responses in isolated rat airways." American Journal of Physiology-Lung Cellular and Molecular Physiology 258, no. 4 (April 1, 1990): L232—L237. http://dx.doi.org/10.1152/ajplung.1990.258.4.l232.
Full textAbstract:
We hypothesized that metabolites of O2 may play a role in the development of airway hyperreactivity and undertook this study to examine the effects of one of these metabolites, hydrogen peroxide (H2O2), on electrical field stimulation-induced contractile responses of isolated rat intrapulmonary bronchi. Exposure to H2O2 (1 mM) elicited a transient contractile response with a peak response equivalent to 18.1 +/- 2.0% of the reference contraction obtained to electrical stimulation. The H2O2-induced contraction was attenuated by pretreatment of tissues with indomethacin and superoxide dismutase, but abolished by catalase and mianserin. Subsequent to H2O2 exposure, electrical field stimulation-induced contractile responses were potentiated (P less than 0.0001), whereas acetylcholine-induced contractions were not. The potentiating effects of H2O2 were inhibited by catalase and mianserin. Addition of 5-hydroxytryptamine (5-HT) to the bath similarly potentiated contractions to electrical stimulation (P less than 0.0001). Together, these results are consistent with a role for 5-HT in H2O2-induced contraction and the subsequent potentiation of airway smooth muscle contraction elicited by cholinergic nerve activation. Thus endogenous metabolites of O2 may be important in modulating airway smooth muscle tone.
12
AlMohimeed, Ibrahim, and Yuu Ono. "Ultrasound Measurement of Skeletal Muscle Contractile Parameters Using Flexible and Wearable Single-Element Ultrasonic Sensor." Sensors 20, no. 13 (June 27, 2020): 3616. http://dx.doi.org/10.3390/s20133616.
Full textAbstract:
Skeletal muscle is considered as a near-constant volume system, and the contractions of the muscle are related to the changes in tissue thickness. Assessment of the skeletal muscle contractile parameters such as maximum contraction thickness ( T h ), contraction time ( T c ), contraction velocity ( V c ), sustain time ( T s ), and half-relaxation ( T r ) provides valuable information for various medical applications. This paper presents a single-element wearable ultrasonic sensor (WUS) and a method to measure the skeletal muscle contractile parameters in A-mode ultrasonic data acquisition. The developed WUS was made of double-layer polyvinylidene fluoride (PVDF) piezoelectric polymer films with a simple and low-cost fabrication process. A flexible, lightweight, thin, and small size WUS would provide a secure attachment to the skin surface without affecting the muscle contraction dynamics of interest. The developed WUS was employed to monitor the contractions of gastrocnemius (GC) muscle of a human subject. The GC muscle contractions were evoked by the electrical muscle stimulation (EMS) at varying EMS frequencies from 2 Hz up to 30 Hz. The tissue thickness changes due to the muscle contractions were measured by utilizing a time-of-flight method in the ultrasonic through-transmission mode. The developed WUS demonstrated the capability to monitor the tissue thickness changes during the unfused and fused tetanic contractions. The tetanic progression level was quantitatively assessed using the parameter of the fusion index (FI) obtained. In addition, the contractile parameters ( T h , T c , V c , T s , and T r ) were successfully extracted from the measured tissue thickness changes. In addition, the unfused and fused tetanus frequencies were estimated from the obtained FI-EMS frequency curve. The WUS and ultrasonic method proposed in this study could be a valuable tool for inexpensive, non-invasive, and continuous monitoring of the skeletal muscle contractile properties.
13
Lou, F., N. A. Curtin, and R. C. Woledge. "Elastic energy storage and release in white muscle from dogfish scyliorhinus canicula." Journal of Experimental Biology 202, no. 2 (January 15, 1999): 135–42. http://dx.doi.org/10.1242/jeb.202.2.135.
Full textAbstract:
The production of work by the contractile component (CC) and the storage and release of work in the elastic structures that act in series (the series elastic component, SEC) with the contractile component were measured using white muscle fibres from the dogfish Scyliorhinus canicula. Heat production was also measured because the sum of work and heat is equivalent to the energy cost of the contraction (ATP used). These energy fluxes were evaluated in contractions with constant-velocity shortening either during stimulation or during relaxation. The muscle preparation was tetanized for 0.6 s and shortened by 1 mm (approximately 15 % of L0) at 3.5 or 7.0 mm s-1 (approximately 15 or 30 % of V0), where L0 is the muscle length at which isometric force is greatest and V0 is the maximum velocity of shortening. In separate experiments, the stiffness of the SEC was characterized from measurements of force responses to step changes in the length of contracting muscle. Using the values of SEC stiffness, we evaluated separately the work and heat associated with the CC and with the SEC. The major findings were (1) that work stored in the SEC could be completely recovered as external work when shortening occurred during relaxation (none of the stored work being degraded into heat) and (2) that, when shortening occurred progressively later during the contraction, the total energy cost of the contraction declined towards that of an isometric contraction.
14
Kato, Tatsuya, Atsushi Sasaki, Hikaru Yokoyama, Matija Milosevic, and Kimitaka Nakazawa. "Effects of neuromuscular electrical stimulation and voluntary commands on the spinal reflex excitability of remote limb muscles." Experimental Brain Research 237, no. 12 (October 10, 2019): 3195–205. http://dx.doi.org/10.1007/s00221-019-05660-6.
Full textAbstract:
Abstract It is well known that contracting the upper limbs can affect spinal reflexes of the lower limb muscle, via intraneuronal networks within the central nervous system. However, it remains unknown whether neuromuscular electrical stimulation (NMES), which can generate muscle contractions without central commands from the cortex, can also play a role in such inter-limb facilitation. Therefore, the objective of this study was to compare the effects of unilateral upper limb contractions using NMES and voluntary unilateral upper limb contractions on the inter-limb spinal reflex facilitation in the lower limb muscles. Spinal reflex excitability was assessed using transcutaneous spinal cord stimulation (tSCS) to elicit responses bilaterally in multiple lower limb muscles, including ankle and thigh muscles. Five interventions were applied on the right wrist flexors for 70 s: (1) sensory-level NMES; (2) motor-level NMES; (3) voluntary contraction; (4) voluntary contraction and sensory-level NMES; (5) voluntary contraction and motor-level NMES. Results showed that spinal reflex excitability of ankle muscles was facilitated bilaterally during voluntary contraction of the upper limb unilaterally and that voluntary contraction with motor-level NMES had similar effects as just contracting voluntarily. Meanwhile, motor-level NMES facilitated contralateral thigh muscles, and sensory-level NMES had no effect. Overall, our results suggest that inter-limb facilitation effect of spinal reflex excitability in lower limb muscles depends, to a larger extent, on the presence of the central commands from the cortex during voluntary contractions. However, peripheral input generated by muscle contractions using NMES might have effects on the spinal reflex excitability of inter-limb muscles via spinal intraneuronal networks.
15
Faas, Henryk, Geoffrey S. Hebbard, Christine Feinle, Patrik Kunz, James G. Brasseur, K. Indireshkumar, John Dent, et al. "Pressure-geometry relationship in the antroduodenal region in humans." American Journal of Physiology-Gastrointestinal and Liver Physiology 281, no. 5 (November 1, 2001): G1214—G1220. http://dx.doi.org/10.1152/ajpgi.2001.281.5.g1214.
Full textAbstract:
Understanding of the control mechanisms underlying gastric motor function is still limited. The aim of the present study was to evaluate antral pressure-geometry relationships during gastric emptying slowed by intraduodenal nutrient infusion and enhanced by erythromycin. In seven healthy subjects, antral contractile activity was assessed by combined dynamic magnetic resonance imaging and antroduodenal high-resolution manometry. After intragastric administration of a 20% glucose solution (750 ml), gastric motility and emptying were recorded during intraduodenal nutrient infusion alone and, subsequently, combined with intravenous erythromycin. Before erythromycin, contraction waves were antegrade (propagation speed: 2.7 ± 1.7 mm/s; lumen occlusion: 47 ± 14%). Eighty-two percent (51/62) of contraction waves were detected manometrically. Fifty-four percent of contractile events (254/473) were associated with a detectable pressure event. Pressure and the degree of lumen occlusion were only weakly correlated ( r 2 = 0.02; P = 0.026). After erythromycin, episodes of strong antroduodenal contractions were observed. In conclusion, antral contractions alone do not reliably predict gastric emptying. Erythromycin induces strong antroduodenal contractions not necessarily associated with fast emptying. Finally, manometry reliably detects ∼80% of contraction waves, but conclusions from manometry regarding actual contractile activity must be made with care.
16
Tamura, Yuki, Karina Kouzaki, Takaya Kotani, and Koichi Nakazato. "Electrically stimulated contractile activity-induced transcriptomic responses and metabolic remodeling in C2C12 myotubes: twitch vs. tetanic contractions." American Journal of Physiology-Cell Physiology 319, no. 6 (December 1, 2020): C1029—C1044. http://dx.doi.org/10.1152/ajpcell.00494.2019.
Full textAbstract:
The contraction of myotubes using electrical pulse stimulation is a research tool used to mimic muscle contractile activity and exercise in rodents and humans. Most protocols employed in previous work used low-frequency twitch contractions. However, high-frequency tetanus contractions that are more physiologically relevant to muscle contractions in vivo are poorly characterized. In this report, the similarities and differences in acute responses and chronic adaptations with different contractile modes using twitches (2 Hz, continuous, 3 h) and tetanus (66 Hz, on: 5 s/off: 5 s, 3 h) were investigated. RNA sequencing-based transcriptome analysis and subsequent bioinformatics analysis suggest that tetanus may promote bioenergetic remodeling rather than twitch. Based on in silico analyses, metabolic remodeling after three contractile sessions of twitch and tetanus were investigated. Although twitch and tetanus had no significant effect on glycolysis, both types of contraction upregulated glucose oxidation capacity. Both twitch and tetanus qualitatively caused mitochondrial adaptations (increased content, respiratory chain enzyme activity, and respiratory function). The magnitude of adaptation was much greater under tetanus conditions. Our findings indicate that the contraction of myotubes by tetanus may be a useful experimental model, especially in the study of metabolic adaptations in C2C12 myotubes.
17
Wang, Wei, Zhanna Nepiyushchikh, David C. Zawieja, Sanjukta Chakraborty, Scott D. Zawieja, Anatoliy A. Gashev, Michael J. Davis, and Mariappan Muthuchamy. "Inhibition of myosin light chain phosphorylation decreases rat mesenteric lymphatic contractile activity." American Journal of Physiology-Heart and Circulatory Physiology 297, no. 2 (August 2009): H726—H734. http://dx.doi.org/10.1152/ajpheart.00312.2009.
Full textAbstract:
Muscular lymphatics use both phasic and tonic contractions to transport lymph for conducting their vital functions. The molecular mechanisms regulating lymphatic muscle contractions are not well understood. Based on the well-established finding that the phosphorylation of myosin light chain 20 (MLC20) plays an essential role in blood vessel smooth muscle contraction, we investigated if phosphorylated MLC20 (pMLC20) would modulate the tonic and/or phasic contractions of lymphatic muscle. The effects of ML-7, a MLC kinase inhibitor (1–10 μM), were tested on the contractile parameters of isolated and cannulated rat mesenteric lymphatics during their responses to the known modulators, pressure (1–5 cmH2O) and substance P (SP; 10−7 M). Immunohistochemical and Western blot analyses of pMLC20 were also performed on isolated lymphatics. The results showed that 1) increasing pressure decreased both the lymphatic tonic contraction strength and pMLC20-to-MLC20 ratio; 2) SP increased both the tonic contraction strength and phosphorylation of MLC20; 3) ML-7 decreased both the lymphatic tonic contraction strength and pMLC20-to-MLC20 ratio; and 4) the increase in lymphatic phasic contraction frequency in response to increasing pressure was diminished by ML-7; however, the phasic contraction amplitude was not significantly altered by ML-7 either in the absence or presence of SP. These data provide the first evidence that tonic contraction strength and phasic contraction amplitude of the lymphatics can be differentially regulated, whereby the increase in MLC20 phosphorylation produces an activation in the tonic contraction without significant changes in the phasic contraction amplitude. Thus, tonic contraction of rat mesenteric lymphatics appears to be MLC kinase dependent.
18
Herdmann, J., P. Enck, P. Zacchi-Deutschbein, and U. Ostermann. "Speed and pressure characteristics of external anal sphincter contractions." American Journal of Physiology-Gastrointestinal and Liver Physiology 269, no. 2 (August 1, 1995): G225—G231. http://dx.doi.org/10.1152/ajpgi.1995.269.2.g225.
Full textAbstract:
The principle of isochronism reflects constant contraction time for varying strengths of muscle contraction. This principle was studied for the innervation of the pelvic floor in humans using motor-evoked potentials (MEPs) and evoked pressure curves (EPCs) from the external anal sphincter muscle (EAS). MEPs and EPCs were simultaneously recorded after transcranial magnetic stimulation of the motor cortex. Voluntary contractions were also studied. Contraction times of the EAS were significantly longer in voluntary contractions (mean, 237 ms) than in EPCs (mean, 90 ms). Depending on either mode of contraction, contraction times varied only slightly despite a wide range of contraction strengths. It is shown that the contractile behavior of the EAS is a function of slow- and fast-twitch muscle fiber distribution and that the principle of isochronism governs motor performance not only of limb muscles but also of the EAS. There exists a unique optimal working range of each muscle to meet its individual function. Disturbance of this principle results in a less efficient contraction with either inappropriate basic tone or disturbed reflex activation in the EAS. Both are possible causes of incontinence.
19
Hasibuan, Zainuddin. "Contractions Used in “Maleficent” Movie." Journal Polingua : Scientific Journal of Linguistics, Literature and Education 2, no. 2 (October 25, 2016): 15–23. http://dx.doi.org/10.30630/polingua.v6i2.82.
Full textAbstract:
The tiltle of this research is “Contractions Used in Maleficent Movie”. “Maleficent” movie was directed by Robert Stromberg based on the originally story Disney's Sleeping Beauty La Belle au bois dormant by Charles Perrault. The background of this research, there are many contractions in “Maleficent” movie. This is good to learn and to use them (contractions) in daily life and maybe they are not found in other movies. The contraction spoken by movie players is sometimes very difficult to understand. The researcher choose this movie because this movie is so interest and inspire. The problem of this research is what contractions are used by the author in the movie “Maleficent” and how are contractions used by the author in the movie “Maleficent”. The purpose of this research is to find out contractions used by the author in the movie “Maleficent” and to explain contractions used by the author in the movie “Maleficent”. To achieve that purpose, the researcher conducted the qualitative research by library research. There are many contractions used by the author which can be classified into eight categories. The most dominant contraction is contracted pronoun. The second is verb contractions. The third are contracting not and ambiguous contraction. The fourth are negative contractions and contraction in tag question. The fifth are contracted noun and beware homophones.
20
Waldrop, T. G., and R. W. Stremel. "Muscular contraction stimulates posterior hypothalamic neurons." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, no. 2 (February 1, 1989): R348—R356. http://dx.doi.org/10.1152/ajpregu.1989.256.2.r348.
Full textAbstract:
Recent studies have suggested that the subthalamic locomotor region (STLR) of the posterior hypothalamus is involved in modulating cardiorespiratory responses to feedback from contracting muscles. The purpose of this study was to determine whether neurons in this hypothalamic region alter their discharge frequency during contraction of hindlimb muscles. Stainless steel electrodes were used to record single-unit activity of STLR neurons during static and rhythmic contractions of hindlimb muscles in anesthetized cats. Recordings were also made from neurons in areas outside but surrounding the subthalamic locomotor region. Contraction of the triceps surae muscles was induced by stimulation of the peripheral cut ends of the L7 and S1 ventral roots. Both static and rhythmic contractions of the triceps surae evoked an increase in the discharge rate of the majority of the STLR cells studied. Two types of excitatory responses were observed: 1) abrupt increases in discharge frequency at the onset of muscular contraction and 2) a delayed more gradual increase in firing. Most of the cells that responded to muscular contraction could be activated by mechanical probing of the triceps surae muscles. However, the changes in discharge frequency were unrelated to changes in arterial pressure occurring during muscular contraction. Most of the neurons located outside the STLR were slightly inhibited by or did not respond to muscular contraction. Thus input from contracting muscles exerts predominantly an excitatory effect on neurons in the posterior hypothalamus. These results are consistent with other studies which have concluded that this hypothalamic site is involved in influencing the cardiorespiratory responses to muscular contraction.
21
Slabaugh, Jessica L., Lucia Brunello, Sandor Gyorke, and Paul M. L. Janssen. "Contractile parameters and occurrence of alternans in isolated rat myocardium at supra-physiological stimulation frequency." American Journal of Physiology-Heart and Circulatory Physiology 302, no. 11 (June 1, 2012): H2267—H2275. http://dx.doi.org/10.1152/ajpheart.01004.2011.
Full textAbstract:
The cardiac refractory period prevents the heart from tetanic activation that is typically used in noncardiac striated muscle tissue. To what extent the refractory period prevents successive action potentials to activate the excitation-contraction coupling process and contractile machinery at supra-physiological rates, such as those present during ventricular fibrillation, is unknown. Using multicellular trabeculae isolated from rat hearts, we studied amplitude and kinetics of contraction at rates well above the normal in vivo rat heart range. We show that even at twice the maximal heart rate of the rat, little or no mechanical instability is observed; twitch contractions are at steady state, albeit with an elevated active diastolic force. Although the amplitude of contraction increased within in vivo heart rates (positive force-frequency response), at frequencies beyond the maximal heart rate (10–30 Hz) a steady decline of contractile amplitude is observed. Not until 30 Hz do the majority of the isolated muscle preparations show mechanical alternans, where strong and weak beats alternate. Interestingly, unlike striated limb skeletal muscle, fusing of twitch contractions did not cause a continuous increase in peak force: at frequencies of 10 Hz and above, systolic force declines with relatively little elevation in diastolic force. Contractile kinetics continued to accelerate, from 1 Hz up to 30 Hz, whereas the relative speed of contraction and relaxation remained closely coupled, reflected by a singular linear relationship between the maximal and minimal derivative of force (dF/d t). We conclude that cardiac muscle can produce mechanically stable steady-state contractions at supra-physiological pacing rates, while these contractions continue to decline in amplitude and increase in diastolic force past maximal heart rate.
22
Kelley, C., P. D'Amore, H. B. Hechtman, and D. Shepro. "Microvascular pericyte contractility in vitro: comparison with other cells of the vascular wall." Journal of Cell Biology 104, no. 3 (March 1, 1987): 483–90. http://dx.doi.org/10.1083/jcb.104.3.483.
Full textAbstract:
Collagen lattices containing bovine retinal pericytes (RPs), vascular smooth muscle cells (VSMCs), pulmonary microvessel endothelial cells (PMECs), or aortic endothelial cells (AECs) were prepared and contraction was quantitated by measuring the resulting change in lattice area. VSMCs were the most efficient at lattice contraction followed by RPs and then PMECs. AECs did not contract the lattices. To document further that these observations represent contraction, cells were grown on inert silicone rubber sheets. Substratum wrinkling was indicative of tension development and quantitated as percent of cells contracted. RPs were more contractile than PMECs, and AECs were incapable of developing tension. VSMCs were less contractile than RPs, unlike the comparative contractility observed with the lattice system. Alteration of actin-containing filaments by cytochalasin B significantly reduced RP contraction of silicone rubber and inhibited their contraction of collagen lattices in a dose-dependent manner. Rhodamine-phalloidin staining of contracting RPs revealed microfilament bundle orientations that suggested their association in the force applied for contraction. RP, VSMC and PMEC contraction of collagen lattices was directly proportional to the concentration of fetal calf serum. Also, RP contraction was greater in calf serum than calf plasma-derived serum, an indication that RPs respond to substances that appear continuously and episodically in blood. These in vitro findings support the theory that pericytes in vivo are contractile but that endothelial cells may also contribute to microvascular tonus.
23
Xu, Hao, Ping Zhao, Wen-Jing Zhang, Jun-Ying Qiu, Li Tan, Xiao-Cao Liu, Qian Wang, et al. "Generation and Role of Oscillatory Contractions in Mouse Airway Smooth Muscle." Cellular Physiology and Biochemistry 47, no. 4 (2018): 1546–55. http://dx.doi.org/10.1159/000490873.
Full textAbstract:
Background/Aims: Tetraethylammonium chloride (TEA) induces oscillatory contractions in mouse airway smooth muscle (ASM); however, the generation and maintenance of oscillatory contractions and their role in ASM are unclear. Methods: In this study, oscillations of ASM contraction and intracellular Ca2+ were measured using force measuring and Ca2+ imaging technique, respectively. TEA, nifedipine, niflumic acid, acetylcholine chloride, lithium chloride, KB-R7943, ouabain, 2-Aminoethoxydiphenyl borate, thapsigargin, tetrodotoxin, and ryanodine were used to assess the mechanism of oscillatory contractions. Results: TEA induced depolarization, resulting in activation of L-type voltage-dependent Ca2+ channels (LVDCCs) and voltage-dependent Na+ (VNa) channels. The former mediated Ca2+ influx to trigger a contraction and the latter mediated Na+ entry to enhance the contraction via activating LVDCCs. Meanwhile, increased Ca2+-activated Cl- channels, inducing depolarization that resulted in contraction through LVDCCs. In addition, the contraction was enhanced by intracellular Ca2+ release from Ca2+ stores mediated by inositol (1,4,5)-trisphosphate receptors (IP3Rs). These pathways together produce the contractile phase of the oscillatory contractions. Furthermore, the increased Ca2+ activated the Na+-Ca2+ exchanger (NCX), which transferred Ca2+ out of and Na+ into the cells. The former induced relaxation and the latter activated Na+/K+-ATPase that induced hypopolarization to inactivate LVDCCs causing further relaxation. This can also explain the relaxant phase of the oscillatory contractions. Moreover, the depolarization induced by VNa channels and NCX might be greater than the hypopolarization caused by Na+/K+-ATPase alone, inducing LVDCC activation and resulting in further contraction. Conclusions: These data indicate that the TEA-induced oscillatory contractions were cooperatively produced by LVDCCs, VNa channels, Ca2+-activated Cl- channels, NCX, Na+/K+ ATPase, IP3Rs-mediated Ca2+ release, and extracellular Ca2+.
24
Honoré, E., M. M. Adamantidis, B. A. Dupuis, C. E. Challice, and P. Guilbault. "Calcium channels and excitation–contraction coupling in cardiac cells. I. Two components of contraction in guinea-pig papillary muscle." Canadian Journal of Physiology and Pharmacology 65, no. 9 (September 1, 1987): 1821–31. http://dx.doi.org/10.1139/y87-284.
Full textAbstract:
Biphasic contractions have been obtained in guinea-pig papillary muscle by inducing partial depolarization in K+-rich solution (17 mM) containing 0.3 μM isoproterenol; whereas in guinea-pig atria, the same conditions led to monophasic contractions corresponding to the first component of contraction in papillary muscle. The relationships between the amplitude of the two components of the biphasic contraction and the resting membrane potential were sigmoidal curves. The first component of contraction was inactivated for membrane potentials less positive than those for the second component. In Na+-low solution (25 mM), biphasic contraction became monophasic subsequent to the loss of the second component, but tetraethylammonium unmasked the second component of contraction. The relationship between the amplitude of the first component of contraction and the logarithm of extracellular Ca2+ concentration was complex, whereas for the second component it was linear. When Ca2+ ions were replaced by Sr2+ ions, only the second component of contraction was observed. It is suggested that the first component of contraction may be triggered by a Ca2+ release from sarcoplasmic reticulum, induced by the fast inward Ca2+ current and (or) by the depolarization. The second component of contraction may be due to a direct activation of contractile proteins by Ca2+ entering the cell along with the slow inward Ca2+ current and diffusing through the sarcoplasm. These results do not exclude the existence of a third "tonic" component, which could possibly be mixed with the second component of contraction.
25
Thomas, G. D., J. Hansen, and R. G. Victor. "Inhibition of alpha 2-adrenergic vasoconstriction during contraction of glycolytic, not oxidative, rat hindlimb muscle." American Journal of Physiology-Heart and Circulatory Physiology 266, no. 3 (March 1, 1994): H920—H929. http://dx.doi.org/10.1152/ajpheart.1994.266.3.h920.
Full textAbstract:
Previous studies have produced conflicting evidence as to whether sympathetic vasoconstriction is impaired in active skeletal muscle. Because alpha 2-, not alpha 1-, adrenergic vasoconstriction is attenuated by mild acidosis, we hypothesized that alpha 2-mediated sympathetic vasoconstriction would be attenuated in contracting glycolytic muscle, which produces more acidosis than oxidative muscle. We compared effects of lumbar sympathetic nerve stimulation and alpha-adrenergic agonists on arterial pressure, femoral blood flow, and force output during contractions of oxidative or glycolytic muscles in anesthetized rats. We found that 1) sympathetic vasoconstriction was preserved during contractions of oxidative soleus muscle and during low-intensity contractions of glycolytic gastrocnemiusplantaris muscles but was abolished during maximal contractions of these glycolytic muscles; 2) this sympatholytic effect was caused by impaired alpha 2-, not alpha 1-, vasoconstriction; and 3) the increased muscle blood flow resulting from a combination of impaired vasconstriction and increased arterial pressure was paralleled by increased force of gastrocnemius-plantaris muscle contraction. Thus contraction-induced impairment of alpha 2-vasoconstriction can augment muscle blood flow and muscle contraction, but the degree of impairment depends on fiber type and intensity of muscle contraction.
26
Pelaez, Nancy J., Tracey R. Braun, Richard J. Paul, Richard A. Meiss, and C. Subah Packer. "H2O2 mediates Ca2+- and MLC20phosphorylation-independent contraction in intact and permeabilized vascular muscle." American Journal of Physiology-Heart and Circulatory Physiology 279, no. 3 (September 1, 2000): H1185—H1193. http://dx.doi.org/10.1152/ajpheart.2000.279.3.h1185.
Full textAbstract:
One purpose of the current study was to establish whether vasoconstriction occurs in all vessel types in response to H2O2. Isometric force was measured in pulmonary venous and arterial rings, and isobaric contractions were measured in mesenteric arteries and veins in response to H2O2. A second purpose was to determine whether H2O2-induced contraction is calcium independent. The addition of H2O2 to calcium-depleted (using the Ca2+ ionophore ionomycin in zero calcium EGTA buffer) muscle caused contraction. Furthermore, permeabilized muscle contracted in response to H2O2 even in zero Ca2+. The final purpose was to determine whether the 20-kDa regulatory myosin light chain (MLC20) phosphorylation plays a role in H2O2-induced contraction. Pulmonary arterial strips were freeze-clamped at various time points during H2O2-induced contractions, and the relative amounts of phosphorylated MLC20 were measured. H2O2 caused dose-dependent contractions that were independent of MLC20 phosphorylation. ML-9, a myosin light chain kinase inhibitor, had no effect on the H2O2 contractile response. In conclusion, H2O2 induces Ca2+- and MLC20 phosphorylation-independent contraction in pulmonary and systemic arterial and venous smooth muscle.
27
Herrera, Gerald M., Thomas J. Heppner, and Mark T. Nelson. "Regulation of urinary bladder smooth muscle contractions by ryanodine receptors and BK and SK channels." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 279, no. 1 (July 1, 2000): R60—R68. http://dx.doi.org/10.1152/ajpregu.2000.279.1.r60.
Full textAbstract:
This study examines the roles of voltage-dependent Ca2+ channels (VDCC), ryanodine receptors (RyRs), large-conductance Ca2+-activated K+ (BK) channels, and small-conductance Ca2+-activated K+ (SK) channels in the regulation of phasic contractions of guinea pig urinary bladder smooth muscle (UBSM). Nisoldipine (100 nM), a dihydropyridine inhibitor of VDCC, abolished spontaneous UBSM contractions. Ryanodine (10 μM) increased contraction frequency and thereby integrated force and, in the presence of the SK blocker apamin, had a greater effect on integrated force than ryanodine alone. Blocking BK (iberiotoxin, 100 nM) or SK (apamin, 100 nM) channels increased contraction amplitude and duration but decreased frequency. The contractile response to iberiotoxin was more pronounced than to apamin. The increases in contraction amplitude and duration to apamin were substantially augmented with ryanodine pretreatment. These results indicate that BK and SK channels have prominent roles as negative feedback elements to limit UBSM contraction amplitude and duration. RyRs also appear to play a significant role as a negative feedback regulator of contraction frequency and duration, and this role is influenced by the activity of SK channels.
28
Goodyear, L. J., P. A. King, M. F. Hirshman, C. M. Thompson, E. D. Horton, and E. S. Horton. "Contractile activity increases plasma membrane glucose transporters in absence of insulin." American Journal of Physiology-Endocrinology and Metabolism 258, no. 4 (April 1, 1990): E667—E672. http://dx.doi.org/10.1152/ajpendo.1990.258.4.e667.
Full textAbstract:
To study the interactions between insulin and contraction on the skeletal muscle glucose transport system, the hindquarters of male rats were perfused in the absence of insulin, in the presence of insulin (30 mU/ml), during contractions induced by sciatic nerve stimulation, or during contractions plus insulin. Compared with control preparations, rates of glucose uptake in the perfused hindquarter were increased by 2.5- and 2.6-fold in the insulin and insulin plus contraction groups, respectively, but not significantly increased in the contraction only preparations. After perfusion, soleus and red and white gastrocnemius muscles from the hindquarter were pooled and used for the preparation of plasma membranes. Skeletal muscle plasma membrane vesicle glucose transport rates were 2.2 +/- 0.5, 7.9 +/- 1.7, 9.0 +/- 2.2, and 10.8 +/- 2.0 nmol.mg protein-1.s-1 (40 mM glucose), and plasma membrane glucose transporter numbers were 4.7 +/- 0.5, 8.1 +/- 0.9, 9.1 +/- 1.0, and 8.6 +/- 0.6 pmol/mg protein in the control, contraction, insulin, and insulin plus contraction groups, respectively. The transport-transporter ratio, an indication of plasma membrane glucose transporter intrinsic activity, was increased by contraction, insulin, and insulin plus contraction. These results demonstrate that contractile activity in the absence of insulin increases muscle plasma membrane glucose transport by increasing transporter number and intrinsic activity. In addition, under these experimental conditions, the effects of insulin and contraction to increase muscle glucose transport are not additive.
29
Sosnowska, Anna J., Aleksandra Vuckovic, and Henrik Gollee. "Automated semi-real-time detection of muscle activity with ultrasound imaging." Medical & Biological Engineering & Computing 59, no. 9 (August 16, 2021): 1961–71. http://dx.doi.org/10.1007/s11517-021-02407-w.
Full textAbstract:
AbstractUltrasound imaging (USI) biofeedback is a useful therapeutic tool; however, it relies on qualitative assessment by a trained therapist, while existing automatic analysis techniques are computationally demanding. This study aims to present a computationally inexpensive algorithm based on the difference in pixel intensity between USI frames. During an offline experiment, where data was analyzed after the study, participants performed isometric contractions of the gastrocnemius medialis (GM) muscle, as executed (30% of maximum contraction) or attempted (low force contraction up to a point when the participant is aware of exerting force or contracting the muscle) movements, while USI, EMG, and force data were recorded. The algorithm achieved 99% agreement with EMG and force measurements for executed movements and 93% for attempted movements, with USI detecting 1.9% more contractions than the other methods. In the online study, participants performed GM muscle contractions at 10% and 30% of maximum contraction, while the algorithm provided visual feedback proportional to the muscle activity (based on USI recordings during the maximum contraction) in less than 3 s following each contraction. We show that the participants reached the target consistently, learning to perform precise contractions. The algorithm is reliable and computationally very efficient, allowing real-time applications on standard computing hardware. It is a suitable method for automated detection, quantification of muscle contraction, and to provide biofeedback which can be used for training of targeted muscles, making it suitable for rehabilitation. Graphical abstract Biofeedback session based on ultrasound imaging (USI) during muscle training. Novel, computationally inexpensive algorithm based on the difference in pixel intensity between USI frames is used to process the video and provide quantitative feedback on the strength of muscle contraction.
30
Zawieja, D. C., K. L. Davis, R. Schuster, W. M. Hinds, and H. J. Granger. "Distribution, propagation, and coordination of contractile activity in lymphatics." American Journal of Physiology-Heart and Circulatory Physiology 264, no. 4 (April 1, 1993): H1283—H1291. http://dx.doi.org/10.1152/ajpheart.1993.264.4.h1283.
Full textAbstract:
The propagation and coordination of lymphatic contractions were studied in the mesentery of the rat small intestine using in situ microscopic observation. Indexes of lymphatic diameter were simultaneously measured at two adjacent lymphangions in spontaneously contracting lymphatics (n = 51). Diameter index, contraction frequency, and the percentage of the intersegmental contractions that were propagated and coordinated (PP) were determined at both sites. The conduction velocity of the contractile activity and the percentage of the coordinated contractions that were propagated both antegrade to the direction of lymph flow and retrograde to the flow stream were determined. The results indicate that 1) 80-90% of the lymphatic contractions in the vessels we evaluated were propagated, 2) the wave of contractile activity propagated both centrally and peripherally, and 3) the conduction velocity of the contractile activity was approximately 4-8 mm/s. We tested the hypothesis that gap junctional communication is responsible for the coordination of the contractile event. To accomplish this, we used the gap junction blockers n-heptanol and oleic acid. PP was 90 +/- 4% under normal conditions and fell to a minimum value of 55 +/- 7% during the gap junction blockade. These results indicate that gap junctional communication played an important role in the propagation and coordination of contractions that occurred in spontaneously active lymphatics.
31
Pal, Anupam, and James G. Brasseur. "The Mechanical Advantage of Local Longitudinal Shortening on Peristaltic Transport." Journal of Biomechanical Engineering 124, no. 1 (September 24, 2001): 94–100. http://dx.doi.org/10.1115/1.1427700.
Full textAbstract:
Whereas bolus transport along the esophagus results from peristaltic contractions of the circular muscle layer, it has been suggested that local shortening of the longitudinal muscle layer concentrates circular muscle fibers in the region where the highest contractile pressures are required. Here we analyze the mechanical consequences of local longitudinal shortening (LLS) through a mathematical model based on lubrication theory. We find that local pressure and shear stress in the contraction zone are greatly reduced by the existence of LLS. In consequence, peak contractile pressure is reduced by nearly 2/3 at physiological LLS, and this reduction is greatest when peak in LLS is well aligned with peak contractile pressure. We conclude that a peristaltic wave of local longitudinal muscle contraction coordinated with the circular muscle contraction wave has both a great physiological advantage (concentrating circular muscle fibers), and a great mechanical advantage (reducing the level of contractile force required to transport the bolus), which combine to greatly reduce circular muscle tone during esophageal peristalsis.
32
Hansson, Sven Ove. "Kernel contraction." Journal of Symbolic Logic 59, no. 3 (September 1994): 845–59. http://dx.doi.org/10.2307/2275912.
Full textAbstract:
AbstractKernel contraction is a natural nonrelational generalization of safe contraction. All partial meet contractions are kernel contractions, but the converse relationship does not hold. Kernel contraction is axiomatically characterized. It is shown to be better suited than partial meet contraction for formal treatments of iterated belief change.
33
Sekizawa, K., J. Tamaoki, J. A. Nadel, and D. B. Borson. "Enkephalinase inhibitor potentiates substance P- and electrically induced contraction in ferret trachea." Journal of Applied Physiology 63, no. 4 (October 1, 1987): 1401–5. http://dx.doi.org/10.1152/jappl.1987.63.4.1401.
Full textAbstract:
To determine the role of endogenous enkephalinase (EC 3.4.24.11) in regulating peptide-induced contraction of airway smooth muscle, we studied the effect of the enkephalinase inhibitor, leucine-thiorphan (Leu-thiorphan), on responses of isolated ferret tracheal smooth muscle segments to substance P (SP) and to electrical field stimulation (EFS). Leu-thiorphan shifted the dose-response curve to SP to lower concentrations. Atropine or the SP antagonist [D-Pro2,D-Trp7,9]SP significantly inhibited SP-induced contractions in the presence of Leu-thiorphan. Leu-thiorphan increased the contractile responses to EFS dose dependently, an effect that was significantly inhibited by the SP antagonist [D-Pro2,D-Trp7,9]SP. SP, in a concentration that did not cause contraction, increased the contractile responses to EFS. This effect was augmented by Leu-thiorphan dose dependently and was not inhibited by hexamethonium or by phentolamine but was inhibited by atropine. Because contractile responses to acetylcholine were not significantly affected by SP or by Leu-thiorphan, the potentiating effects of SP were probably on presynaptic-postganglionic cholinergic neurotransmission. Captopril, bestatin, or leupeptin did not augment contractions, suggesting that enkephalinase was responsible for the effects. These results suggest that endogenous tachykinins modulate smooth muscle contraction and endogenous enkephalinase modulates contractions produced by endogenous or exogenous tachykinins and tachykinin-induced facilitation of cholinergic neurotransmission.
34
Stebbins, C. L., O. A. Carretero, T. Mindroiu, and J. C. Longhurst. "Bradykinin release from contracting skeletal muscle of the cat." Journal of Applied Physiology 69, no. 4 (October 1, 1990): 1225–30. http://dx.doi.org/10.1152/jappl.1990.69.4.1225.
Full textAbstract:
Results of previous studies from our laboratory suggest that bradykinin has a role in the exercise pressor reflex elicited by static muscle contraction. The purpose of this study was to quantify the release of bradykinin from contracting skeletal muscle. In 18 cats, blood samples were withdrawn directly from the venous effluent of the triceps surae muscles immediately before and after 30 s of static contraction producing peak muscle tensions of 33, 50, and 100% of maximum electrically stimulated contraction. Contractions producing muscle tensions of 50 and 100% of maximum increased muscle venous bradykinin levels by 27 +/- 9 and 19 +/- 10 pg/ml, respectively. Conversely, 33% maximum contraction did not alter muscle venous bradykinin concentrations. However, when captopril was administered to slow the degradation of bradykinin, muscle venous bradykinin increased from 68 +/- 15 pg/ml at rest to 106 +/- 18 after contractions of 33% of maximum. When muscle ischemia was induced by 2 min of arterial occlusion before and during 30 s of 33% of maximum contraction, muscle venous bradykinin increased by 15 +/- 5 pg/ml. In addition, contraction-induced changes in muscle venous pH and lactate strongly correlated with bradykinin concentrations (r = 0.80 and 0.83, respectively). These data demonstrate that static contraction of relatively high intensity evokes the release of bradykinin from skeletal muscle and that ischemia, decreased pH, and increased lactate are strongly correlated with this release.
35
Di Liberto, G., E. Dallot, I. Eude-Le Parco, D. Cabrol, F. Ferré, and M. Breuiller-Fouché. "A critical role for PKCζ in endothelin-1-induced uterine contractions at the end of pregnancy." American Journal of Physiology-Cell Physiology 285, no. 3 (September 2003): C599—C607. http://dx.doi.org/10.1152/ajpcell.00040.2003.
Full textAbstract:
We have previously shown that protein kinase C (PKC) ζ and/or PKCδ are necessary for endothelin-1 (ET-1)-induced human myometrial contraction at the end of pregnancy (Eude I, Paris P, Cabrol D, Ferré F, and Breuiller-Fouché M. Biol Reprod 63: 1567–1573, 2000). Here, we report that the selective inhibitor of PKCδ isoform, Rottlerin, does not prevent ET-1-induced contractions, whereas LY-294002, a phosphatidylinositol (PI) 3-kinase inhibitor, affects the contractile response. This study characterized the in vitro contractile response of cultured human pregnant myometrial cells to ET-1 known to induce in vitro contractions of intact uterine smooth muscle strips. Cultured myometrial cells incorporated into collagen lattices have the capacity to reduce the size of these lattices, referred to as lattice contraction. Neither the selective conventional PKC isoform inhibitor, Gö-6976, or rottlerin affected myometrial cell-mediated gel contraction by ET-1, whereas this effect was blocked by LY-294002. We found that treatment of myometrial cell lattices with an inhibitory peptide specific for PKCζ or with an antisense against PKCζ resulted in a significant loss of ET-1-induced contraction. Evidence is also presented by using confocal microscopy that ET-1 induced translocation of PKCζ to a structure coincident with the actin-rich microfilaments of the cytoskeleton. We have shown that PKCζ has a role in the actin organization in ET-1-stimulated cells. Accordingly, our results suggest that PKCζ plays a role in myometrial contraction in pregnant women.
36
Connelly, Denise M., Charles L. Rice, Martin R. Roos, and Anthony A. Vandervoort. "Motor unit firing rates and contractile properties in tibialis anterior of young and old men." Journal of Applied Physiology 87, no. 2 (August 1, 1999): 843–52. http://dx.doi.org/10.1152/jappl.1999.87.2.843.
Full textAbstract:
The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young (20.8 ± 0.8 yr) and six old men (82.0 ± 1.7 yr). For each subject, data were collected from repeated tests over a 2-wk period. Contractile tests included maximal voluntary contraction (MVC) with twitch interpolation and stimulated twitch contractions. The old men had 26% lower MVC torque ( P < 0.01) than did the young men, but percent activation was not different (99.1 and 99.3%, respectively). Twitch contraction durations were 23% longer ( P < 0.01) in the old compared with the young men. During a series of repeated brief steady-state contractions at 10, 25, 50, 75, and 100% MVC, motor unit firing rates were recorded. Results from ∼950 motor unit trains in each subject group indicated that at all relative torque levels mean firing rates were 30–35% lower ( P < 0.01) in the old subjects. Comparisons between young and old subjects’ mean firing rates at each of 10%, 50%, and MVC torques and their corresponding mean twitch contraction duration yielded a range of moderate-to-high correlations ( r = −0.67 to −0.84). That lower firing rates were matched to longer twitch contraction durations in the muscle of old men, and relatively higher firing rates were matched with shorter contraction times from the young men, indirectly supports the neuromuscular age-related remodeling principle.
37
Gorcheva, Zornitsa V., Galya Ts Stavreva, Negrin N. Negrev, and Radomir G. Radomirov. "Ascending Excitatory and Inhibitory Motor Activity of Colonic Longitudinal and Circular Muscles in Rat Model." Journal of Biomedical and Clinical Research 12, no. 1 (July 1, 2019): 10–18. http://dx.doi.org/10.2478/jbcr-2019-0002.
Full textAbstract:
Summary In this experiment we studied the role of excitatory and inhibitory neurotransmissions in the ascending reflex pathways in isolated rat colon. Partitioned organ bath, electrical field stimulation (EFS), drugs and isolated preparations were used to evaluate motor activity of (LM) and circular muscles (CM). Ascending motor responses of LM and CM were frequency-dependent contraction, significantly more expressed in LM. Atropine (0.3 µM) decreased ascending contractions of LM. During atropine treatment spantide (0.1 µM) further suppressed ascending contractile motor responses. In the presence of atropine, L-NNA (0.5 mM) restored ascending contractions of LM, while contractions were strongly depressed after addition of L-arginine (0.5 mM). Ascending response in CM, caused by atropine, consisted of an initial relaxation followed by contraction. Spantide decreased the contraction. L-NNA reduced the relaxation and significantly restored the atropine-influenced contraction, while L-arginine induced a deep relaxation of CM. The presence of ChAT, SP-containing nerve cell bodies and fibers and NADPH-diaphorase-reactive cell bodies and processes in myenteric ganglia were detected. The results indicated that nitric oxide is an important modulator of ascending cholinergic and tachykininergic excitation in colonic region of the large intestine of rats.
38
Dalton, Brian H., Brad Harwood, Andrew W. Davidson, and Charles L. Rice. "Triceps surae contractile properties and firing rates in the soleus of young and old men." Journal of Applied Physiology 107, no. 6 (December 2009): 1781–88. http://dx.doi.org/10.1152/japplphysiol.00464.2009.
Full textAbstract:
Mean maximal motor unit firing rates (MUFRs) of the human soleus are lower (5–20 Hz) than other limb muscles (20–50 Hz) during brief sustained contractions. With healthy adult aging, maximal MUFRs are 20–40% lower and twitch contractile speed of lower limb muscles are 10–40% slower compared with young adults. However, it is unknown whether the inherently low maximal MUFRs for the soleus are further reduced with aging in association with age-related slowing in contractile properties. The purpose of the present study was to compare the changes in triceps surae contractile properties and MUFRs of the soleus throughout a variety of contraction intensities in six old (∼75 yr old) and six young (∼24 yr old) men. Neuromuscular measures were collected from the soleus and triceps surae during repeated sessions (2–6 sessions). Populations of single MUFR trains were recorded from the soleus with tungsten microelectrodes during separate sustained 6- to 10-s isometric contractions of varying intensities [25%, 50%, 75%, and 100% maximal voluntary isometric contraction (MVC)]. The old men had weaker triceps surae strength (MVC; 35% lower) and slower contractile properties (contraction duration; 20% longer) than the young men. However, there was no difference in average MUFRs of the soleus at 75% and 100% MVC (∼14.5 Hz and ∼16.5 Hz, respectively). At 25% and 50% MVC, average rates were 10% and 20% lower in the old men compared with young, respectively. Despite a significant slowing in triceps surae contraction duration, there was no age-related change in MUFRs recorded at high contractile intensities in the soleus. Thus the relationship between the whole muscle contractile properties and MUFRs found in other muscle groups may not exist between the triceps surae and soleus and may be muscle dependent.
39
Kern, Mark K., Ronald C. Arndorfer, James S. Hyde, and Reza Shaker. "Cerebral cortical representation of external anal sphincter contraction: effect of effort." American Journal of Physiology-Gastrointestinal and Liver Physiology 286, no. 2 (February 2004): G304—G311. http://dx.doi.org/10.1152/ajpgi.00201.2003.
Full textAbstract:
The external anal sphincter (EAS) plays a critical role in maintaining fecal continence; however, cerebral cortical control of voluntary EAS contraction is not completely understood. Our aims were to determine the cortical areas associated with voluntary EAS contraction and to determine the effect of two levels of sphincter contraction effort on brain activity. Seventeen asymptomatic adults (ages 21-48, 9 male) were studied using functional magnetic resonance imaging (fMRI) to detect brain activity. Studies were done in two stages. In stage 1 (10 subjects, 5 male), anal sphincter pressure was monitored from a catheter-affixed bag. Subjects performed maximal and submaximal EAS contractions during two fMRI scanning sessions consisting of alternating 10-s intervals of sustained contraction and rest. In stage 2 studies, seven subjects (4 male) performed only maximum effort sphincter contractions without a catheter. EAS contraction was associated with multifocal fMRI activity in sensory/motor, anterior cingulate, prefrontal, parietal, occipital, and insular regions. Total cortical activity volume was significantly larger ( P < 0.05) for maximal (5,175 ± 720 μl) compared with submaximal effort contractions (2,558 ± 306 μl). Similarly, percent fMRI signal change was significantly higher ( P < 0.05) for maximal (4.8 ± 0.1%) compared with submaximal effort contractions (2.2 ± 0.1%). Cortical region-of-interest analysis showed the incidence of insular activation to be more common in women compared with men. Other cortical regions showed no such gender differences. fMRI activity detected in stage 2 showed similar regions of cortical activation to those of the stage 1 study. Willful contraction of the EAS is associated with multifocal cerebral cortical activity. The volume and intensity of cerebral cortical activation is commensurate with the level of contractile effort.
40
SARNMETA, PANITARN, and SUTHEP SUANTAI. "Global Minimization of best proximity points for semi-cyclic Berinde contractions." Carpathian Journal of Mathematics 34, no. 3 (2018): 411–16. http://dx.doi.org/10.37193/cjm.2018.03.17.
Full textAbstract:
In this paper, we introduce a semi-cyclic Berinde contraction pair on a metric space which is more general than that of semi-cyclic contraction pair defined by Gabeleh and Abkar [Gabeleh, M. and Abkar, A., Best proximity points for semi-cyclic contractive pairs in Banach spaces, Int. Math. Forum, 6 (2011), 2179–2186] and prove an existence result concerning global monomization of best proximity points of this pair. Our main result can be used to obtain a common fixed point theorem of some contractive mappings related to Berinde’s contractions without commutative assumption. An example supporting our main result is also given.
41
Perez, Jose F., and Michael J. Sanderson. "The Contraction of Smooth Muscle Cells of Intrapulmonary Arterioles Is Determined by the Frequency of Ca2+ Oscillations Induced by 5-HT and KCl." Journal of General Physiology 125, no. 6 (May 31, 2005): 555–67. http://dx.doi.org/10.1085/jgp.200409217.
Full textAbstract:
Increased resistance of the small blood vessels within the lungs is associated with pulmonary hypertension and results from a decrease in size induced by the contraction of their smooth muscle cells (SMCs). To study the mechanisms that regulate the contraction of intrapulmonary arteriole SMCs, the contractile and Ca2+ responses of the arteriole SMCs to 5-hydroxytrypamine (5-HT) and KCl were observed with phase-contrast and scanning confocal microscopy in thin lung slices cut from mouse lungs stiffened with agarose and gelatin. 5-HT induced a concentration-dependent contraction of the arterioles. Increasing concentrations of extracellular KCl induced transient contractions in the SMCs and a reduction in the arteriole luminal size. 5-HT induced oscillations in [Ca2+]i within the SMCs, and the frequency of these Ca2+ oscillations was dependent on the agonist concentration and correlated with the extent of sustained arteriole contraction. By contrast, KCl induced Ca2+ oscillations that occurred with low frequencies and were preceded by small, localized transient Ca2+ events. The 5-HT–induced Ca2+ oscillations and contractions occurred in the absence of extracellular Ca2+ and were resistant to Ni2+ and nifedipine but were abolished by caffeine. KCl-induced Ca2+ oscillations and contractions were abolished by the absence of extracellular Ca2+ and the presence of Ni2+, nifedipine, and caffeine. Arteriole contraction was induced or abolished by a 5-HT2–specific agonist or antagonist, respectively. These results indicate that 5-HT, acting via 5-HT2 receptors, induces arteriole contraction by initiating Ca2+ oscillations and that KCl induces contraction via Ca2+ transients resulting from the overfilling of internal Ca2+ stores. We hypothesize that the magnitude of the sustained intrapulmonary SMC contraction is determined by the frequency of Ca2+ oscillations and also by the relaxation rate of the SMC.
42
Mondal, Anupom, Zuoyun Xie, Yuki Miyano, Chihiro Tsutsui, Ichiro Sakata, Yoichi Kawamoto, Sayaka Aizawa, Toru Tanaka, Sen-ichi Oda, and Takafumi Sakai. "Coordination of motilin and ghrelin regulates the migrating motor complex of gastrointestinal motility in Suncus murinus." American Journal of Physiology-Gastrointestinal and Liver Physiology 302, no. 10 (May 15, 2012): G1207—G1215. http://dx.doi.org/10.1152/ajpgi.00379.2011.
Full textAbstract:
Motilin and ghrelin are the gastrointestinal (GI) hormones released in a fasting state to stimulate the GI motility of the migrating motor complex (MMC). We focused on coordination of the ghrelin/motilin family in gastric contraction in vivo and in vitro using the house musk shrew ( Suncus murinus ), a ghrelin- and motilin-producing mammal. To measure the contractile activity of the stomach in vivo, we recorded GI contractions either in the free-moving conscious or anesthetized S. murinus and examined the effects of administration of motilin and/or ghrelin on spontaneous MMC in the fasting state. In the in vitro study, we also studied the coordinative effect of these hormones on the isolated stomach using an organ bath. In the fasting state, phase I, II, and III contractions were clearly recorded in the gastric body (as observed in humans and dogs). Intravenous infusion of ghrelin stimulated gastric contraction in the latter half of phase I and in the phase II in a dose-dependent manner. Continuous intravenous infusion of ghrelin antagonist (d-Lys3-GHRP6) significantly suppressed spontaneous phase II contractions and prolonged the time of occurrence of the peak of phase III contractions. However, intravenous infusion of motilin antagonist (MA-2029) did not inhibit phase II contractions but delayed the occurrence of phase III contractions of the MMC. In the in vitro study, even though a high dose of ghrelin did not stimulate contraction of stomach preparations, ghrelin administration (10−10-10−7 M) with pretreatment of a low dose of motilin (10−10 M) induced gastric contraction in a dose-dependent manner. Pretreatment with 10−8 M ghrelin enhanced motilin-stimulated gastric contractions by 10 times. The interrelation of these peptides was also demonstrated in the anesthetized S. murinus . The results suggest that ghrelin is important for the phase II contraction and that coordination of motilin and ghrelin are necessary to initiate phase III contraction of the MMC.
43
James, Arlene N., James P. Ryan, and Henry P. Parkman. "Inhibitory effects of botulinum toxin on pyloric and antral smooth muscle." American Journal of Physiology-Gastrointestinal and Liver Physiology 285, no. 2 (August 2003): G291—G297. http://dx.doi.org/10.1152/ajpgi.00296.2002.
Full textAbstract:
Botulinum toxin injection into the pylorus is reported to improve gastric emptying in gastroparesis. Classically, botulinum toxin inhibits ACh release from cholinergic nerves in skeletal muscle. The aim of this study was to determine the effects of botulinum toxin on pyloric smooth muscle. Guinea pig pyloric muscle strips were studied in vitro. Botulinum toxin type A was added; electric field stimulation (EFS) was performed every 30 min for 6 h. ACh (100 μM)-induced contractile responses were determined before and after 6 h. Botulinum toxin caused a concentration-dependent decrease of pyloric contractions to EFS. At a low concentration (2 U/ml), botulinum toxin decreased pyloric contractions to EFS by 43 ± 9% without affecting ACh-induced contractions. At higher concentrations (10 U/ml), botulinum toxin decreased pyloric contraction to EFS by 75 ± 7% and decreased ACh-induced contraction by 79 ± 9%. In conclusion, botulinum toxin inhibits pyloric smooth muscle contractility. At a low concentration, botulinum toxin decreases EFS-induced contractile responses without affecting ACh-induced contractions suggesting inhibition of ACh release from cholinergic nerves. At higher concentrations, botulinum toxin directly inhibits smooth muscle contractility as evidenced by the decreased contractile response to ACh.
44
Balshaw, Thomas G., Garry J. Massey, Thomas M. Maden-Wilkinson, Neale A. Tillin, and Jonathan P. Folland. "Training-specific functional, neural, and hypertrophic adaptations to explosive- vs. sustained-contraction strength training." Journal of Applied Physiology 120, no. 11 (June 1, 2016): 1364–73. http://dx.doi.org/10.1152/japplphysiol.00091.2016.
Full textAbstract:
Training specificity is considered important for strength training, although the functional and underpinning physiological adaptations to different types of training, including brief explosive contractions, are poorly understood. This study compared the effects of 12 wk of explosive-contraction (ECT, n = 13) vs. sustained-contraction (SCT, n = 16) strength training vs. control ( n = 14) on the functional, neural, hypertrophic, and intrinsic contractile characteristics of healthy young men. Training involved 40 isometric knee extension repetitions (3 times/wk): contracting as fast and hard as possible for ∼1 s (ECT) or gradually increasing to 75% of maximum voluntary torque (MVT) before holding for 3 s (SCT). Torque and electromyography during maximum and explosive contractions, torque during evoked octet contractions, and total quadriceps muscle volume (QUADSVOL) were quantified pre and post training. MVT increased more after SCT than ECT [23 vs. 17%; effect size (ES) = 0.69], with similar increases in neural drive, but greater QUADSVOL changes after SCT (8.1 vs. 2.6%; ES = 0.74). ECT improved explosive torque at all time points (17–34%; 0.54 ≤ ES ≤ 0.76) because of increased neural drive (17–28%), whereas only late-phase explosive torque (150 ms, 12%; ES = 1.48) and corresponding neural drive (18%) increased after SCT. Changes in evoked torque indicated slowing of the contractile properties of the muscle-tendon unit after both training interventions. These results showed training-specific functional changes that appeared to be due to distinct neural and hypertrophic adaptations. ECT produced a wider range of functional adaptations than SCT, and given the lesser demands of ECT, this type of training provides a highly efficient means of increasing function.
45
Yin, Xiaoyan, Nicholas J. D. Gower, Howard A. Baylis, and Kevin Strange. "Inositol 1,4,5-Trisphosphate Signaling Regulates Rhythmic Contractile Activity of Myoepithelial Sheath Cells in Caenorhabditis elegans." Molecular Biology of the Cell 15, no. 8 (August 2004): 3938–49. http://dx.doi.org/10.1091/mbc.e04-03-0198.
Full textAbstract:
Intercellular communication between germ cells and neighboring somatic cells is essential for reproduction. Caenorhabditis elegans oocytes are surrounded by and coupled via gap junctions to smooth muscle-like myoepithelial sheath cells. Rhythmic sheath cell contraction drives ovulation and is triggered by a factor secreted from oocytes undergoing meiotic maturation. We demonstrate for the first time that signaling through the epidermal growth factor-like ligand LIN-3 and the LET-23 tyrosine kinase receptor induces ovulatory contractions of sheath cells. Reduction-of-function mutations in the inositol 1,4,5-trisphosphate (IP3) receptor gene itr-1 and knockdown of itr-1 expression by RNA interference inhibit sheath contractile activity. itr-1 gain-of-function mutations increase the rate and force of basal contractions and induce tonic sheath contraction during ovulation. Sheath contractile activity is disrupted by RNAi of plc-3, one of six phospholipase C-encoding genes in the C. elegans genome. PLC-3 is a PLC-γ homolog and is expressed in contractile sheath cells of the proximal gonad. Maintenance of sheath contractile activity requires plasma membrane Ca2+ entry. We conclude that IP3 generated by LET-23 mediated activation of PLC-γ induces repetitive intracellular Ca2+ release that drives rhythmic sheath cell contraction. Calcium entry may function to trigger Ca2+ release via IP3 receptors and/or refill intracellular Ca2+ stores.
46
Janson, L. W., J. Kolega, and D. L. Taylor. "Modulation of contraction by gelation/solation in a reconstituted motile model." Journal of Cell Biology 114, no. 5 (September 1, 1991): 1005–15. http://dx.doi.org/10.1083/jcb.114.5.1005.
Full textAbstract:
The actin-based cytoskeleton is a dynamic component of living cells with major structural and contractile properties involved in fundamental cellular processes. The action of actin-binding proteins can decrease or increase the gel structure. Changes in the actin-based cytoskeleton have long been thought to modulate the myosin II-based contractions involved in these cellular processes, but there has been some debate concerning whether maximal gelation increases or decreases contractile activity. To address this question, we have examined how contractile activity is modulated by the extent of actin gelation. The model system consists of physiologically relevant concentrations and molar ratios of actin filaments (whose lengths are controlled by gelsolin), the actin-cross-linking protein filamin, and smooth muscle myosin II. This system has been studied at the macroscopic and light microscopic levels to relate the gel structure to the rate of contraction. We present results which show that while a minimal amount of structure is necessary to transmit the contractile force, increasing the gel structure inhibits the rate of contraction, despite an increase in the actin-activated Mg(2+)-ATPase activity of myosin. Decreasing the total myosin concentration also inhibits the rate of contraction. Application of cytochalasin D to one side of the contractile network increases the rate of contraction and also induces movement comparable to flare streaming observed in isolated amoeba cytoplasm. These results are interpreted relative to current models of the relationship between the state of gelation and contraction and to the potential effects of such a relationship in the living cell.
47
Namba, Hitoshi, and Hideaki Tsuchida. "Effect of Volatile Anesthetics with and without Verapamil on Intracellular Activity in Vascular Smooth Muscle." Anesthesiology 84, no. 6 (June 1, 1996): 1465–74. http://dx.doi.org/10.1097/00000542-199606000-00023.
Full textAbstract:
Background Although halothane and isoflurane inhibit receptor agonist-induced smooth muscle contraction by inhibiting Ca2+ influx via the L-type voltage-dependent Ca2+ channels, their effects on pharmacomechanical coupling remained to be clarified. The intracellular action of both anesthetics was studied during agonist-induced contractions using the Ca2+ channel blocker verapamil. Methods Isolated spiral strips of rat thoracic aorta with endothelium removed were suspended for isometric tension recordings in physiologic salt solution. Cytosolic concentration of Ca2+ ([Ca2+]i) was measured concomitantly using fura-2-Ca2+ fluorescence. Muscle contraction was evoked by the receptor agonists with 30 nm norepinephrine or 10 microM prostaglandin F2 alpha (PGF2 alpha), followed by exposure to halothane, at 0%, 1%, 2%, and 3% or isoflurane, at 2% and 4%. The effects of the anesthetics were compared with those of 0.1-1 microM verapamil (n = 8 for each condition). To clarify the intracellular action of the volatile anesthetics on agonist-induced contractions, this procedure was repeated for the anesthetics only in the presence of 1 microM verapamil (n = 8 for each condition). The effects of both anesthetics were also examined in nonreceptor-mediated contractions evoked with a 1-microM dose of the protein kinase C activator, 12-deoxyphorbol 13-isobutylate, which increases the Ca2+ sensitivity of the contractile elements (n = 8 for each). Results Halothane, isoflurane, and verapamil suppressed norepinephrine-and PGF2 alpha-induced increases in muscle tension and [Ca2+]i in a concentration-dependent manner. The Ca2+-tension regression lines suggested that the volatile anesthetics reduced Ca2+ sensitivity of the contractile elements during PGF2 alpha-induced contraction. Pretreatment of the muscle strip with verapamil revealed that halothane and isoflurane released Ca2+ during norepinephrine-induced contraction and that [Ca2+]i-tension relationship was modulated during PGF2 alpha-induced contractions. Halothane at 2% and 3% and isoflurane at 4% suppressed 12-deoxyphorbol 13-isobutylate-induced increases in muscle tension, whereas they enhanced increases in [Ca2+]i, indicating that both anesthetics suppressed Ca2+ sensitivity during 12-deoxyphorbol 13-isobutylate-induced contraction. Conclusions Verapamil pretreatment unmasked the intracellular action of the anesthetics. Halothane and isoflurane influenced pharmacomechanical coupling during agonist-induced contraction.
48
Beaty, O. "Arterial blood pressure control during hindlimb and forelimb contraction in the dog." American Journal of Physiology-Heart and Circulatory Physiology 248, no. 5 (May 1, 1985): H678—H687. http://dx.doi.org/10.1152/ajpheart.1985.248.5.h678.
Full textAbstract:
This study examined the differential reflex cardiovascular responses evoked by separate contractions of the right hindlimb and forelimb and established the mechanism of a regional reflex vasodilation associated with hindlimb skeletal muscle contraction. The two groups of skeletal muscle were contracted separately by electrical stimulation (2-48 Hz) of the peripheral motor nerves. The left nonexercising hindlimb was perfused at constant flow. All blood pressure-regulating mechanisms were intact. Arterial blood pressure (ABP), left nonexercising hindlimb perfusion pressure (HLPP), and heart rate (HR) were recorded. HR was increased by skeletal muscle contraction. This response was independent of muscle group and contraction frequency. Increases in both ABP and HLPP were produced by high-frequency contractions (greater than 16 Hz) of either the hindlimb or forelimb. Decreases were evoked only by hindlimb contractions (greater than 8 Hz). The nonexercising skeletal muscle vascular bed contributed to this systemic depressor response by vasodilating. The mechanism involved a contraction-induced withdrawal of sympathetic nerve activity to that vascular bed. Concomitant with this response was an increase in heart rate that was blocked with propranolol. Similar heart rate changes evoked by forelimb contractions also were blocked with propranolol. These data indicate that sympathetic outflow to resting skeletal muscle depends on the origin and magnitude of the afferent signal from the contracting skeletal muscle.
49
Duchateau, J., and K. Hainaut. "Electrical and mechanical changes in immobilized human muscle." Journal of Applied Physiology 62, no. 6 (June 1, 1987): 2168–73. http://dx.doi.org/10.1152/jappl.1987.62.6.2168.
Full textAbstract:
After forearm fracture, the human thumb was unilaterally immobilized in eight subjects for 6 wk in a standard plaster cast. Changes of contraction properties were studied in the adductor pollicis muscle. The contralateral muscle remained unrestrained and served as control. After immobilization, the maximal voluntary contraction was reduced by 55% (P less than 0.05), and the electrically evoked maximal tetanic contraction (Po) was reduced by 33% (P less than 0.05). The decrease of Po was associated with increased maximal rate of tension development (10%) and decreased maximal rate of tension relaxation (22%). The twitch times to peak and to half relaxation were increased by 16 and 14%, respectively, but the twitch tension (Pt) was not significantly changed and the Pt/Po ratio was increased by 43% after immobilization. The muscle surface action potential presented an increase of its duration (19%) and a decrease of the amplitude and the total area (15 and 26%, respectively). The comparison of the electrical and mechanical alterations recorded during voluntary contractions, and in contractions evoked by electrical stimulation of the motor nerve, suggests that immobilization not only modifies the peripheral processes associated with contraction but also changes central and/or neural command of the contraction. At peripheral sites, it is proposed that the intracellular processes of contraction play the major role in the contractile impairment recorded during immobilization.
50
Hansson, Sven Ove. "Theory contraction and base contraction unified." Journal of Symbolic Logic 58, no. 2 (June 1993): 602–25. http://dx.doi.org/10.2307/2275221.
Full textAbstract:
AbstractOne way to construct a contraction operator for a theory (belief set) is to assign to it a base (belief base) and an operator of partial meet contraction for that base. Axiomatic characterizations are given of the theory contractions that are generated in this way by (various types of) partial meet base contractions.