Artykuły w czasopismach na temat „Single compartment fires”

Fire scars result from the death of the vascular cambium resulting from excessive heating, which exposes sapwood to infection and initiates the wood decay process. In southeastern Ohio, prescribed fires in April 1995 and 1997 scarred Quercus prinus L. and Q. velutina Lam. Low-intensity fires scorched bark and produced scars, primarily on the downslope side of the stem. Eighteen scorched trees (4-23 cm at DBH) were dissected in November 1997, 14 of which had fire scars. The vascular cambium beneath natural bark fissures was most vulnerable to injury. No charred or scorched wood was associated with scars of trees exposed to single fires; wood exposed by scars from the 1995 fire was charred by the 1997 fire. Consistent with the compartmentalization process, discoloration and whiterot occurred within compartment boundaries of wood present at the time of wounding. Scars from the prescribed fires were consistent in size and shape with scars in nearby oak trees previously hypothesized to have been burned prior to 1950.

A comparative study is presented of different calculation methods with respect to the evacuation of smoke and heat in the case of enclosure fires in large compartments. These methods range from manual calculations, based on empirical formulae, over zone modeling to the use of computational fluid dynamics. The focus is on large single storey compartments. The differences between results obtained with the examined methods are discussed. .

Calcium imaging using fura-2 and whole cell recording revealed the effective location of the oscillator mechanism on dopaminergic neurons of the substantia nigra, pars compacta, in slices from rats aged 15–20 days. As previously reported, dopaminergic neurons fired in a slow rhythmic single spiking pattern. The underlying membrane potential oscillation survived blockade of sodium currents with TTX and was enhanced by blockade of voltage-sensitive potassium currents with TEA. Calcium levels increased during the subthreshold depolarizing phase of the membrane potential oscillation and peaked at the onset of the hyperpolarizing phase as expected if the pacemaker potential were due to a low-threshold calcium current and the hyperpolarizing phase to calcium-dependent potassium current. Calcium oscillations were synchronous in the dendrites and soma and were greater in the dendrites than in the soma. Average calcium levels in the dendrites overshot steady-state levels and decayed over the course of seconds after the oscillation was resumed after having been halted by hyperpolarizing currents. Average calcium levels in the soma increased slowly, taking many cycles to achieve steady state. Voltage clamp with calcium imaging revealed the voltage dependence of the somatic calcium current without the artifacts of incomplete spatial voltage control. This showed that the calcium current had little or no inactivation and was half-maximal at −40 to −30 mV. The time constant of calcium removal was measured by the return of calcium to resting levels and depended on diameter. The calcium sensitivity of the calcium-dependent potassium current was estimated by plotting the slow tail current against calcium concentration during the decay of calcium to resting levels at −60 mV. A single compartment model of the dopaminergic neuron consisting of a noninactivating low-threshold calcium current, a calcium-dependent potassium current, and a small leak current reproduced most features of the membrane potential oscillations. The same currents much more accurately reproduced the calcium transients when distributed uniformly along a tapering cable in a multicompartment model. This model represented the dopaminergic neuron as a set of electrically coupled oscillators with different natural frequencies. Each frequency was determined by the surface area to volume ratio of the compartment. This model could account for additional features of the dopaminergic neurons seen in slices, such as slow adaptation of oscillation frequency and may produce irregular firing under different coupling conditions.

This paper compares the activity of hindlimb motor units from muscles mainly composed of fast-twitch muscle fibers (medial and lateral gastrocnemius: MG/LG, tibialis anterior: TA) to motor units from a muscle mainly composed of slow-twitch muscle fibers (soleus: SOL) during unrestrained walking in the conscious rat. Several differences in the activation profiles of motor units from these two groups of muscles were observed. For example, motor units from fast muscles (e.g., MG/LG and TA) fired at very high mean frequencies of discharge, ranging from 60 to 100 Hz, and almost always were recruited with initial doublets or triplets, i.e., initial frequencies ≥100 Hz. In contrast, the majority of SOL units fired at much lower mean rates of discharge, ≈30 Hz, and had initial frequencies of only 30–60 Hz (i.e., there were no initial doublets/triplets ≥100 Hz). Thus the presence of initial doublet or triplets was dependent on the intrinsic properties of the motor unit, i.e., faster units were recruited with a doublet/triplet more often than slower units. Moreover, in contrast to units from the slow SOL muscle, the activity of single motor units from the fast MG/LG muscle, especially units recruited midway or near the end of a locomotor burst, was unrelated to the activity of the remainder of the motoneuron pool, as measured by the corresponding gross-electromyographic (EMG) signal. This dissociation of activity was suggested to arise from a compartmentalized recruitment of the MG/LG motoneuron pool by the rhythm-generating networks of the spinal cord. In contrast, when comparing the rate modulation of simultaneously recorded motor units within a single LG muscle compartment, the frequency profiles of unit pairs were modulated in a parallel fashion. This suggested that the parent motoneurons were responsive to changes in synaptic inputs during unrestrained walking, unlike the poor rate modulation that occurs during locomotion induced from brain stem stimulation. In summary, data from this study provide evidence that the firing behavior of motor units during unrestrained walking is influenced by both the intrinsic properties of the parent motoneuron and by synaptic inputs from the locomotor networks of the spinal cord. In addition, it also provides the first extensive description of motor-unit activity from different muscles during unrestrained walking in the conscious rat.

AbstractThe Aii amacrine cell of mammalian retina collects signals from several hundred rods and is hypothesized to transmit quantal “single-photon” signals at scotopic (starlight) intensities. One problem for this theory is that the quantal signal from one rod when summed with noise from neighboring rods would be lost if some mechanism did not exist for removing the noise. Several features of the Aii might together accomplish such a noise removal operation: The Aii is interconnected into a syncytial network by gap junctions, suggesting a noise-averaging function, and a quantal signal from one rod appears in five Aii cells due to anatomical divergence. Furthermore, the Aii contains voltage-gated Na+ and K+ channels and fires slow action potentials in vitro, suggesting that it could selectively amplify quantal photon signals embedded in uncorrelated noise. To test this hypothesis, we simulated a square array of AII somas (Rm = 25,000 Ohm-cm2) interconnected by gap junctions using a compartmental model. Simulated noisy inputs to the Aii produced noise (3.5 mV) uncorrelated between adjacent cells, and a gap junction conductance of 200 pS reduced the noise by a factor of 2.5, consistent with theory. Voltage-gated Na+ and K+ channels (Na+: 4 nS, K+: 0.4 nS) produced slow action potentials similar to those found in vitro in the presence of noise. For a narrow range of Na+ and coupling conductance, quantal photon events (-5–10 mV) were amplified nonlinearly by subthreshold regenerative events in the presence of noise. A lower coupling conductance produced spurious action potentials, and a greater conductance reduced amplification. Since the presence of noise in the weakly coupled circuit readily initiates action potentials that tend to spread throughout the AII network, we speculate that this tendency might be controlled in a negative feedback loop by up-modulating coupling or other synaptic conductances in response to spiking activity.

The caudal mesopallium (CM) is a cortical-level area in the songbird auditory pathway where selective, invariant responses to familiar songs emerge. To characterize the cell types that perform this computation, we made whole cell recordings from brain slices in juvenile zebra finches ( Taeniopygia guttata) of both sexes. We found three groups of putatively excitatory neurons with distinct firing patterns. Tonic cells produced sustained responses to depolarizing step currents, phasic cells produced only a few spikes at the onset, and an intermediate group was also phasic but responded for up to a few hundred milliseconds. Phasic cells had smaller dendritic fields, higher resting potentials, and strong low-threshold outward rectification. Pharmacological treatment with voltage-gated potassium channel antagonists 4-aminopyridine and α-dendrotoxin converted phasic to tonic firing. When stimulated with broadband currents, phasic cells fired coherently with frequencies up to 20–30 Hz, whereas tonic neurons were more responsive to frequencies around 0–10 Hz. The distribution of peak coherence frequencies was similar to the distribution of temporal modulation rates in zebra finch song. We reproduced these observations in a single-compartment biophysical model by varying cell size and the magnitude of a slowly inactivating, low-threshold potassium current ( ILT). These data suggest that intrinsic dynamics in CM are matched to the temporal statistics of conspecific song. NEW & NOTEWORTHY In songbirds, the caudal mesopallium is a key brain area involved in recognizing the songs of other individuals. This study identifies three cell types in this area with distinct firing patterns (tonic, phasic, and intermediate) that reflect differences in cell size and a low-threshold potassium current. The phasic-firing neurons, which do not have a counterpart in mammalian auditory cortex, are better able to follow rapid modulations at the frequencies found in song.

Here analytical and simulation results are presented characterizing the recoding arising when overlapping patterns of sensor input impinge on an array of model neurons with branched thresholded dendritic trees. Thus, the neural units employed are intended to capture the integrative behavior of pyramidal cells that sustain isolated Na+ or NMDA spikes in their branches. Given a defined set of sensor vectors, equations were derived for the probability of firing of both branches and neurons and for the expected overlap between the neural firing patterns triggered by two afferent patterns of given overlap. Thus, both the sparseness of the neural representation and the orthogonalization of overlapping vectors were computed. Simulations were then performed with an array of 1000 neurons comprising 30,000 branches to verify the analytical results and confirm their applicability to systems (which include any practicable artificial system) in which the combinatorically possible branches and neurons are severely subsampled. A means of readout and a measure of discrimination performance were provided so that the accuracy of discrimination among overlapping sensor vectors could be optimized as a function of neuron structure parameters. Good performance required both orthogonalization of the afferent patterns, so that discrimination was accurate and free of interference, and maintenance of a minimum level of neural activity, so that some neurons fired in response to each sensor pattern. It is shown that the discrimination performance achieved by arrays of neurons with branched dendritic trees could not be reached with single-compartment units, regardless of how many of the latter are used. The analytical results furnish a benchmark against which to measure further enhancements in the performance of subsequent simulated systems incorporating local neural mechanisms which, while often less amenable to closed-form analysis, are ubiquitous in biological neural circuitry.

A stylized, symmetric, compartmental model of a dopamine neuron in vivo shows how rate and pattern can be modulated either concurrently or differentially. If two or more parameters in the model are varied concurrently, the baseline firing rate and the extent of bursting become de-correlated, which provides an explanation for the lack of a tight correlation in vivo and is consistent with some independence of the mechanisms that generate baseline firing rates versus bursts. We hypothesize that most bursts are triggered by a barrage of synaptic input and that particularly meaningful stimuli recruit larger numbers of synapses in a more synchronous way. An example of concurrent modulation is that increasing the short-lived AMPA current evokes additional spikes without regard to pattern, producing comparable increases in spike frequency and fraction fired in bursts. On the other hand, blocking the SK current evokes additional bursts by allowing a depolarization that previously produced only a single spike to elicit two or more and elongates existing bursts by the same principle, resulting in a greater effect on pattern than rate. A probabilistic algorithm for the random insertion of spikes into the firing pattern produces a good approximation to the pattern changes induced by increasing the AMPA conductance, but not by blocking the SK current, consistent with a differential modulation in the latter case. Furthermore, blocking SK produced a longer burst with a greater intra-burst frequency in response to a simulated meaningful input, suggesting that reduction of this current may augment reward-related responses.

Purpose The core needle biopsy (CNB) procedure is an essential part of breast cancer diagnosis. Current CNB devices on the market are not suitable for low-resource settings, which makes early breast cancer diagnosis inaccessible for women in these areas. Disposable CNB devices are the gold standard of breast cancer diagnostic tools in high-income countries, but the single-use cost—approximately $40 to $200—is unaffordable in low- and middle-income countries. Existing reusable devices are susceptible to internal contamination as blood travels back through the coaxial needle into the driver and thus requires laborious cleaning procedures. Methods After conducting more than 100 interviews with stakeholders at 18 hospitals in the United States, South Africa, and Peru, we devised criteria for the device. The device must prevent internal driver contamination and match the standard tissue sample size. We report the design and development of a reusable CNB device with disposable needles that trap contamination. To demonstrate where blood travels in current reusable devices and prove that internal contamination can be completely eliminated, we created an external attachment that interfaces with the Bard Magnum, an existing reusable driver that yields internal contamination. To prove our concept, we evaluated contamination rates by placing water-indicating tape inside the Bard driver and firing the device into a plastic test tube that was filled with blood-mimicking solutions and covered with a latex glove. Results When we fired the existing Bard Magnum device without our attachment, contaminants entered the internal compartment of the device both times, as shown by the water-indicating tape; however, when the device was fired with our external needle attachment, the water-indicating tape was completely clean, which verified that there was no internal contamination. Conclusion We can conclude from our contamination testing that blood enters the device as a result of contaminants traveling back between the faces of the needle and sheath into the device’s driver and that our external attachment eliminates this risk. Using these insights, we are currently developing a full reusable driver device with novel disposable needles that trap contamination to remove safety concerns associated with reusable devices, lower procedural cost, and increase access to breast cancer diagnostic tools in low-resource settings. AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST The following represents disclosure information provided by authors of this manuscript. All relationships are considered compensated. Relationships are self-held unless noted. I = Immediate Family Member, Inst = My Institution. Relationships may not relate to the subject matter of this manuscript. For more information about ASCO's conflict of interest policy, please refer to www.asco.org/rwc or ascopubs.org/jco/site/ifc . Megan Callanan Employment: Stryker Spine Patents, Royalties, Other Intellectual Property: Ithemba LLC Laura Hinson Patents, Royalties, Other Intellectual Property: Ithemba LLC Madeline Lee Patents, Royalties, Other Intellectual Property: Ithemba LLC Sophia Triantis Patents, Royalties, Other Intellectual Property: Ithemba LLC Amir Manbachi Research Funding: Siemens Healthineers (Inst) Susan Harvey Honoraria: Hologic Inc, IBM Watson Imaging Consulting or Advisory Role: IBM Watson, Hologic Inc Research Funding: IBM Watson

Abstract Background Perianal fistulizing disease (PFD) is a complication occurring in about 20% of Crohn’s Disease (CD) patients. It consists of the formation of new epithelised tracks connecting the intestine with the outer perianal region, which dramatically worsens a patient's quality of life. The mechanisms driving fistula formation have not been elucidated and therefore, there are currently no specific treatments for PFD. Methods We collected rectum biopsies of CD patients with and without PFD in the absence of rectal inflammation (CD and CD+PFD), and with active rectal inflammation (CDinf and CD+PFDinf) (Fig.1). Rectal tissue samples were processed for RT-qPCR, or histologic analysis, and single-cell RNA sequencing (scRNAseq) for each patient. Results Differential expression gene (DEG) analysis of CD4+ and CD8+ T cells comparing CD vs CD+PFD and CDinf vs CD+PFDinf patients, respectively, revealed increased expression of TGFB1 in patients with fistulae. To investigate the main cellular subsets TGFB1 was interacting with, we performed ligand-receptor interaction analysis using CellphoneDB, which indicated that T-cell derived TGFB1 was primary interacting with the stromal compartment (Fig.2). 365 DEG were found in lamina propria (LP) fibroblasts of CD+PFD compared to CD, including TGFβ1-inducible genes such as TFPI2, SERPINE2 and MMPs 1 and 3. These changes were validated by bulk RT-qPCR, underscoring their potential use as PFD biomarkers (Fig.3). Moreover, we also identified a signature of elastin fibre assembly genes dysregulated in CD+PFD fibroblasts, suggesting molecular changes in the formation of elastin fibres in these patients. To determine whether the differentiation of fibroblasts was altered in the context of PFD, we conducted trajectory analysis using RNA velocity. Whilst fibroblasts in CD patients preferentially differentiate towards myofibroblasts, patients with PFD are biased towards LP fibroblasts, indicating an overall structural rearrangement of the mesenchyme in the rectum of patients with PFD, regardless of their inflammatory status (Fig.4). Importantly, analysis of an independent scRNAseq dataset of CD and ulcerative colitis (UC) patients showed higher expression of TGFB1 in T cells of active CD compared to active UC patients, suggesting that these alterations are already present in CD patients before the onset of a fistulizing phenotype and might potentially contribute to explain the absence of PFD in UC patients. Conclusion Based on these results, we suggest that the rectum of patients suffering from PFD present cellular and transcriptomic differences compared to CD patients without PFD. These changes are inflammation independent and point towards the TGFβ pathway as the main driver of this complication.

1. A detailed compartmental model of a cerebellar Purkinje cell with active dendritic membrane was constructed. The model was based on anatomic reconstructions of single Purkinje cells and included 10 different types of voltage-dependent channels described by Hodgkin-Huxley equations, derived from Purkinje cell-specific voltage-clamp data where available. These channels included a fast and persistent Na+ channel, three voltage-dependent K+ channels, T-type and P-type Ca2+ channels, and two types of Ca(2+)-activated K+ channels. 2. The ionic channels were distributed differentially over three zones of the model, with Na+ channels in the soma, fast K+ channels in the soma and main dendrite, and Ca2+ channels and Ca(2+)-activated K+ channels in the entire dendrite. Channel densities in the model were varied until it could reproduce Purkinje cell responses to current injections in the soma or dendrite, as observed in slice recordings. 3. As in real Purkinje cells, the model generated two types of spiking behavior. In response to small current injections the model fired exclusively fast somatic spikes. These somatic spikes were caused by Na+ channels and repolarized by the delayed rectifier. When higher-amplitude current injections were given, sodium spiking increased in frequency until the model generated large dendritic Ca2+ spikes. Analysis of membrane currents underlying this behavior showed that these Ca2+ spikes were caused by the P-type Ca2+ channel and repolarized by the BK-type Ca(2+)-activated K+ channel. As in pharmacological blocking experiments, removal of Na+ channels abolished the fast spikes and removal of Ca2+ channels removed Ca2+ spiking. 4. In addition to spiking behavior, the model also produced slow plateau potentials in both the dendrite and soma. These longer-duration potentials occurred in response to both short and prolonged current steps. Analysis of the model demonstrated that the plateau potentials in the soma were caused by the window current component of the fast Na+ current, which was much larger than the current through the persistent Na+ channels. Plateau potentials in the dendrite were carried by the same P-type Ca2+ channel that was also responsible for Ca2+ spike generation. The P channel could participate in both model functions because of the low-threshold K2-type Ca(2+)-activated K+ channel, which dynamically changed the threshold for dendritic spike generation through a negative feedback loop with the activation kinetics of the P-type Ca2+ channel. 5. These model responses were robust to changes in the densities of all of the ionic channels.(ABSTRACT TRUNCATED AT 400 WORDS)

1. L4 and L5 dorsal root ganglia of rats aged 4-5 wk were isolated in vitro with their dorsal roots and sciatic nerves intact. With the use of intracellular microelectrodes, conduction velocity (CV) was determined along both peripheral and central axons and active and passive membrane properties were investigated with the use of a single-electrode switching clamp. 2. Neurons were classified into one of the three subgroups, A alpha/beta, A delta, and C, on the basis of a combination of axonal CV and action potential duration. Soma diameters overlapped between these groups. 3. Action potentials elicited by nerve stimulation in all cells and by a somatic current step in A alpha/beta-cells were always blocked by tetrodotoxin (TTX) 0.1-1 microM), whereas somatic action potentials in a proportion of A delta-cells and all C cells were TTX-resistant. 4. Passive electrical properties differed significantly between A alpha/beta-, A delta-, and C cells. The contribution of the additional membrane of the axons to the recorded electrical properties was analyzed with the use of a compartmental model of the neurons (see APPENDIX). 5. Most neurons discharged only a single action potential at the onset of a depolarizing current step, but 33% of A alpha/beta-cells fired repetitively throughout the step. This was associated with a lower threshold for action potential initiation by depolarizing current and a shorter afterhyperpolarization than in other A alpha/beta-cells. 6. Afterhyperpolarizations varied in size and duration between neurons and most were either not or only slightly affected by replacing Ca2+ in the bathing solution with Co2+ or Ba2+ or by adding tetraethylammonium (1 and 10 mM). Outward tail currents following an active response could be fitted with one fast exponential (time constant = 13 +/- 1 ms, mean +/- SE) and, in 65% of cells, one to three slower time course currents (to which exponentials with time constants of approximately 50, 300, or 1,500 ms could be fitted). A very slow late-onset current (detected in 33% of C cells) resembled a Ca(2+)-dependent K+ conductance described in several other neurons. 7. Voltage transients showed "sag" during maintained hyperpolarizing current steps in 90% of A alpha/beta-cells and 70% of A delta-cells but only 13% of C cells. Time-dependent inward currents were recorded when membrane potential was hyperpolarized. These currents had mean activation time constants of approximately 40 ms at -120 mV and were Cs+ sensitive and Ba2+ insensitive. 8. The proportion of neurons with a transient outward current, IA, increased as CV decreased (36% of A alpha/beta-cells, 56% of A delta-cells, 63% of C cells). Outward currents in cells of all subgroups had either one or two of three inactivation time constants (means approximately 22, 120, and 800 ms). 9. This study shows that many of the electrical characteristics of isolated dorsal root ganglion neurons can be demonstrated in intact ganglia in which the neurons can be better identified functionally. The currents underlying the afterhyperpolarization in these cells are diverse across all subgroups and require further investigation. The electrical effects of retaining the axonal projections of the cells and the use of microelectrodes filled with 0.5 M KC1 are discussed in relation to the differences from data recorded in dissociated neurons.

Abstract Background Tebipenem pivoxil hydrobromide (tebipenem HBr), an orally (PO) bioavailable prodrug of tebipenem, is a carbapenem with broad-spectrum activity against Gram-positive and -negative bacteria that is being developed for the treatment of patients with complicated urinary tract infections, including AP. Data from a one-compartment in vitro infection model demonstrated that the ratio of free-drug plasma area under the curve (AUC) to MIC with adjustment for dosing interval (τ) (AUC:MIC ratio•1/τ) was the PK-PD index most associated with tebipenem HBr efficacy [VanScoy BD et al., IDWeek 2019, Poster 1565]. Studies were undertaken to characterize the magnitude of tebipenem HBr free-drug plasma AUC:MIC ratio•1/τ associated with efficacy for Enterobacteriaceae using a neutropenic murine AP model. Methods A single dose pharmacokinetic study was completed in neutropenic mice infected via intra-renal injection with 104 CFU/kidney of Escherichia coli NCTC 13441. Following PO administration of 4 tebipenem HBr doses (1, 15, 45 and 100 mg/kg), plasma samples were collected at 0.25, 0.5, 1, 2, 4, 6 and 8 hours post-treatment initiation and drug concentrations were determined using LC/MS/MS. Dose-ranging studies were completed using a panel of 7 Enterobacteriaceae isolates (tebipenem HBr MIC values of 0.015 to 0.5 mg/L). Mice were infected with 104 CFU/kidney via intra-renal injection. Two hours post-incubation, 8 total daily tebipenem HBr doses (0.3 to 135 mg/kg) were fractionated into regimens given every 8 hours. The relationship between change in log10 CFU/g from baseline at 24 hours and free-drug plasma AUC:MIC ratio•1/τ was fit using a Hill-type model. Free-drug plasma AUC:MIC ratio•1/τ values associated with net bacterial stasis and 1- and 2-log10 CFU/g reductions from baseline at 24 hours were determined. Results The relationship between change in log10 CFU/g from baseline at 24 hours and tebipenem HBr free-drug plasma AUC:MIC ratio•1/τ described the data well (r2 = 0.833). Free-drug plasma AUC:MIC ratio•1/τ values associated with net bacterial stasis and a 1-log10 CFU/g reduction from baseline were 26.2 and 54.1, respectively. A 2-log10 CFU/g reduction was not achieved. Relationship between change in log10 CFU/g from baseline at 24 hours and tebipenem HBr free-drug plasma AUC:MIC ratio•1/τ based on data for a panel of Enterobacteriaceae isolates evaluated in the dose-ranging studies conducted using a neutropenic murine acute pyelonephritis model Conclusion These data will be useful to support tebipenem HBr dose selection for clinical studies in patients with AP. Disclosures Brian D. VanScoy, B.S., Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Steven Fikes, BA, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Christopher M. Rubino, PharMD, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Sujata M. Bhavnani, PharMD, MS, FIDSA, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Nicole S. Cotroneo, BS, Spero Therapeutics (Employee, Shareholder) Ian A. Critchley, PhD, Spero Therapeutics (Employee, Shareholder) Thomas R. Parr, PhD, Spero Therapeutics (Employee, Shareholder) Paul G. Ambrose, PharMD, FIDSA, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support)

Summary The Ac zone refers to the sandstone facies of the Wara formation, which belongs to the Wasia group of the Middle Cretaceous age.* Owing to variable shale to sand ratios, the Ac zone is realized as different isolated sand lenses scattered all over the field. Owing to the complexity of the geology and the flow mechanism, well testing was used to manage the reservoir. The concept of a sequence of well tests on the same well was found to be essential in improving the oil recovery. Conducted on a specific well situated within a closed sand lens, sequential well testing yielded valuable information that assisted in understanding the drive mechanism and the deteriorating reservoir parameters, permeability, and skin. Such a method was crucial in improving the recovery from the sand lens as well as from the single-well-treatment perspective. This paper presents an example of how such a technique aided in improving the oil recovery from a small sand lens. Introduction Sequential well testing has played an important role in understanding the flow mechanism and the damage evolution in a dynamic sense within a sand lens. Computer-aided analysis of these well tests has resulted in better geological modeling and simulation, which further led to improved oil recovery. Sequential well testing was very effective in understanding the pressure-support mechanism, permeability deterioration, and increase in skin around wells. The tests further revealed the geological boundaries around the well. The geological setting was used as a quality-control parameter to ensure the consistency of all tests. A simulation model was constructed, taking into account well-test results, and it confirmed the strong influence of faulting on the production performance, which in this case is causing poor pressure support and a quick water breakthrough. Based on these results, the model was used to improve the sweep efficiency of the sand lens by exploring different schemes. Discussion Geology. The Ac zone refers to the sandstone facies of the Wara formation in the Bahrain field. It belongs to the Wasia group of the Middle Cretaceous age. The Wara in the Bahrain field varies from 60 to 95 ft in thickness, and the sand interval varies from 0 to 60 ft. Owing to variable shale to sand ratios, the Ac zone is realized as different isolated sand lenses scattered all over the field. Each sand lens varies in shape and size and acts as a trap for original oil accumulations and transferals from other zones; hence, it must be studied and optimized individually. For the purpose of this paper, a study of a small sand lens is presented. This sand lens (Fig. 1) is located in the northwest area of the Bahrain field. Its net thickness varies from 0 to 32 ft, and permeability varies from 0 md at the edges to 150 md at the center of the lens. The production behavior of anomalous wells (explained later) within the sand lens indicates that the sand body is cut by at least two sealing faults, making at least three isolated compartments. The sand lens is overlain and underlain by shale, making it an almost closed system; this is shown by the poor pressure support caused by faulting and juxtapositions with other zones. Production Behavior. It was observed that three nearby wells located within the same sand lens produce and behave differently. While Well 453 is an oil producer, Wells 376 and 244 are water and high-gas producers, respectively. A conceptual geological model that can provide an explanation for such behavior is shown in Fig. 2. This model was thought of originally but was changed later based on well tests. Sequential Well Testing. Six buildups were carried out on Well 453, which provided a good monitoring of the reservoir and a better understanding of the changes in reservoir behavior in terms of permeability deterioration, damage evolution, and pressure behavior. The main conclusion with regard to the geological setting was the fact that the sand body consisted of noncommunicating compartments; all tests clearly detected nearby combinations of faults and barriers. This allowed us to concentrate on developing the compartments more efficiently at a minimum cost. Table 1 shows the results of these buildups. It can be seen clearly from the table that the skin evolves at the sandface, causing a direct deterioration in the production rate. The increase in skin damage from 2.4 in the beginning of the well's life to 7.1 after 2 years is attributed to a combination of the following:Emulsion blocking. This is a main contributor to the skin problem in the Ac reservoir. This is evident by the more than 100% improvement seen after the well is treated with surfactant wash. However, the surfactant wash effect diminishes quickly as emulsion forms again around the wellbore, necessitating periodic treatments.Fines movement into the wellbore and blockage of the pore throats. This was proven by core testing, as shown in Fig. 3.**The swelling of clays caused by water encroachment into the area (water cut has increased from 0 to 25% in 5 years). X-ray diffraction (XRD) analysis of a typical Ac sand core is shown in Table 2. Lab testing concluded that the last two observations are most probably related because the presence of 10 to 20% kaolinite results in the problem of fines mobilization. The loose attachment of kaolinite plates to host grains causes fluid turbulence within a pore to dislodge delicately attached kaolinite, as shown in Figs. 4a and 4b. The loosened kaolinite plates then migrate to pore throats, where they lodge and act as a check valve.*** This means that skin evolution is triggered by a certain critical high flow rate. Fig. 5a shows the actual permeability deterioration before the initiation of the water-support scheme and the conducting of surfactant wash treatments. Geology. The Ac zone refers to the sandstone facies of the Wara formation in the Bahrain field. It belongs to the Wasia group of the Middle Cretaceous age. The Wara in the Bahrain field varies from 60 to 95 ft in thickness, and the sand interval varies from 0 to 60 ft. Owing to variable shale to sand ratios, the Ac zone is realized as different isolated sand lenses scattered all over the field. Each sand lens varies in shape and size and acts as a trap for original oil accumulations and transferals from other zones; hence, it must be studied and optimized individually. For the purpose of this paper, a study of a small sand lens is presented. This sand lens (Fig. 1) is located in the northwest area of the Bahrain field. Its net thickness varies from 0 to 32 ft, and permeability varies from 0 md at the edges to 150 md at the center of the lens. The production behavior of anomalous wells (explained later) within the sand lens indicates that the sand body is cut by at least two sealing faults, making at least three isolated compartments. The sand lens is overlain and underlain by shale, making it an almost closed system; this is shown by the poor pressure support caused by faulting and juxtapositions with other zones. Production Behavior. It was observed that three nearby wells located within the same sand lens produce and behave differently. While Well 453 is an oil producer, Wells 376 and 244 are water and high-gas producers, respectively. A conceptual geological model that can provide an explanation for such behavior is shown in Fig. 2. This model was thought of originally but was changed later based on well tests.

Abstract Background Platelet concentrates (PCs) are stored at room temperature to preserve their biological activity. To minimize the risk of bacterial outgrowth, storage time is limited to 7 days. It is well-established that prolonged storage of PCs results in modifications that result in a decreased hemostatic efficacy. This loss of platelet functionality during storage is commonly referred to as the platelet storage lesion (PSL). Typical events linked to development of the PSL are shape changes, platelet activation and loss of receptors crucial for platelet functionality. Two-dimensional (2D) differential gel electrophoresis (DIGE), isotope tagging and isotope-coded affinity tagging (ICAT) have been previously used to monitor changes in protein composition during storage. These studies have provided valuable insights into the changes associated with the PSL, however, these studies generally focused on a limited set of proteins. Aim We aimed to generate an overview of changes in the platelet proteome during storage using label free quantitative mass spectrometry. Furthermore, we employed Gene ontology (GO) enrichment analysis to identify pathways and biological processes that were linked to development of the PSL. Methods Three independently pooled PCs were stored in plasma under standard blood bank conditions for 16 days. Tryptic peptides were separated by nanoscale C18 reverse phase chromatography coupled on line to an Orbitrap Fusion Tribrid mass spectrometer. The RAW mass spectrometry files were processed with the MaxQuant computational platform. The global changes in protein level during platelet storage were assessed employing the analysis-of-variance functions of PERSEUS. Gene ontology enrichment analysis of biological processes, molecular functions and cellular compartments of the significantly different proteins was performed using the Cytoscape plug-in BiNGO. Results A total number of 2501 proteins was detected in all 3 biological replicates in at least one of the time points analyzed. The analysis showed that 18 proteins were down-regulated over time, whereas the level of 3 proteins was found to increase. CytoScape BinGo analysis of these significantly downregulated proteins revealed that the majority of this set was linked to GO-terms platelet degranulation, secretion and regulated exocytosis. This set of proteins included von Willebrand factor (VWF), serglycin (SRGN), SPARC, amyloid beta A4 protein (APP), multimerin-1 (MMRN1) and platelet factor 4 (PF4). A significant decline in these protein levels was observed at day 5 of storage, suggesting that release of α-granules is a relatively early event during platelet storage. At day 5 also a marked decline in S100A9 was observed. S100A9 has been implicated in degranulation in neutrophils, and may therefore also be linked to platelet granule release. Levels of membrane surface platelet glycoproteins such as glycoprotein Ibα did not significantly change at day 5. Only one single protein, histone H2A, was found to be consistently decreased already at two days of storage, but the significance of this finding is not clear. Upon prolonged storage (13 and 16 days) an increase in the level of α-2-macroglobulin (A2M), immunoglobulin M (IGM) and glycogenin-1 (GYG1) was observed suggesting that platelets acquire an (increased) potential to bind and/or internalize proteins from their environment. Consistent with this notion we also detected significant levels of several serine protease inhibitors, although levels of these proteins did not change upon storage. Conclusions Overall, our findings highlight dynamic changes in protein composition of platelets during storage. Our data provide evidence for sustained release of α-granules over time which becomes significant at day 5. Our data also suggest that during storage, platelets can bind or ingest proteins from their environment which may have impact on the hemostatic properties of stored platelets. Disclosures Leebeek: CSL Behring: Membership on an entity's Board of Directors or advisory committees, Research Funding; Baxalta: Consultancy, Membership on an entity's Board of Directors or advisory committees; Dutch Hemphilia Foundation: Research Funding.

Abstract Abstract 1294 Poster Board I-316 Background Unfortunately, whatever is initially used, 10-20% bleeding events in haemophilia patients with high-responding inhibitors cannot be controlled by bypassing agents. Sequential combined by-passing therapy (SCBT), the sequential alternate administration of recombinant activated factor VII (rFVIIa) and activated prothrombin complex concentrate (APCC) was reported to have a synergistic effect on thrombin generation and to be successful in 5 children with haemophilia and inhibitors with bleeds unresponsive to replacement and by-passing therapy with a single agent (Schneiderman et al, Haemophilia 2007;13:244-8). No information was available on safety and efficacy of SCBT in adult patients or for post-surgical bleeding. We report a survey promoted by the European Haemophilia Treatment Standardisation Board (EHTSB) on 11 SCBT courses in children and adults. Methods A web-based database was prepared in order to collect retrospective data on SCBT courses in a standardised and anonymous manner from patients' files. SCBT was defined as the administration of rFVIIa and APCC within 12 hours from each other. Results Eleven patients with high titre inhibitors underwent SCBT: 9 with haemophilia A and 2 with haemophilia B. Four were children aged 9-14 years (mean age: 10 years), and 7 were adults aged 24-45 years (mean age: 34 years). Two of the 4 children were suffering from knee joint bleeds refractory to high doses of rFVIIa (up to 270 μg/Kg/2 hours) and to high doses of APCC (up to 80 U/Kg /8 hours); another child had a calf bleed refractory to rFVIIa (270 mcg/kg /6 hours). The remaining child had a post-surgical bleed after an arthroscopic synovectomy treated for 3 days with rFVIIa 125 mcg/Kg every 2 hours. Five adults had undergone major surgery (removal of knee prosthesis, knee arthrodesis, total knee joint replacement, laparoscopic cholecystectomy and laparotomy for kidney rupture), initially treated with rFVIIa from 90 up to 270 mcg/Kg every 2 hours, and followed by significant bleed. One of these patients was switched to APCC 80 U/Kg every8 hours without success. An adult had a lower limb compartmental syndrome unresponsive to rFVIIa 180 mcg/Kg every 3 hours for 5 times and to FEIBA 75 U/Kg every 8 hours. Another adult had a post-traumatic muscle and joint bleed in the upper limb getting worse after 4 administrations of 200 mcg/Kg every 4 hours. SCT was administered in children and adults alternating one APCC dose to one to 3 rFVIIa doses: the intervals between an APCC dose and an rFVIIa dose ranged from 3 to 6 hours. APCC dosing ranged from 20 to 80 U/Kg every 8 to 12 hours. rFVIIa dosing ranged from 80 to 270 μg/Kg every 3 to 12 hours. Major bleeding control was achieved in 12-24 hours of SCBT in all patients. SCBT was discontinued after 1 to 15 days and patients underwent prophylaxis with FEIBA or rFVIIa for 2 to 28 days. No clinical adverse event was observed, but a rise of D-dimer levels occurred in 3 of 5 tested patients, without consumption of platelet and/or fibrinogen. Conclusions This survey reports 11 SCBT courses in 7 adults and 4 children to treat unresponsive bleeds after 6 major surgical procedures, 3 joint bleeds and 2 muscle bleeds. SCBT was efficacious without clinical adverse events; nevertheless it remains a salvage treatment for its potential risks. These data represent a sound background in order to plan a prospective clinical trial that is needed to confirm these findings and provide more solid evidence. Disclosures No relevant conflicts of interest to declare.

In modern aero-engines, the lubrication system plays a key role due to the demand for high reliability. Oil is used not only for the lubrication of bearings, gears, or seals but it also removes large amounts of the generated heat. Also, air from the compressor at elevated temperature is used for sealing the bearing chambers and additional heat is introduced into the oil through radiation, conduction, and convection from the surroundings. The impact of excessive heat on the oil may lead to severe engine safety and reliability problems which can range from oil coking (carbon formation) to oil fires. Coking may lead to a gradual blockage of the oil tubes and subsequently increase the internal bearing chamber pressure. As a consequence, oil may migrate through the seals into the turbomachinery and cause contamination of the cabin air or ignite and cause failure of the engine. It is therefore very important for the oil system designer to be capable to predict the system’s functionality. Coking or oil ignition may occur not only inside the bearing chamber but also in the oil pipes which carry away the air and oil mixture from the bearing chamber. Bearing chambers usually have one pipe (vent pipe) at the top of the chamber and also one pipe (scavenge pipe) at the bottom which is attached to a scavenge pump. The vent pipe enables most of the sealing air to escape thus avoid over-pressurization in the bearing compartment. In a bearing chamber, sealing air is the dominant medium in terms of volume occupation and also in terms of causing expansion phenomena. The scavenge pipe carries away most of the oil from the bearing chamber but some air is also carried away. The heat transfer in vent pipes was investigated by Busam (2004, “Druckverlust und Wärmeuebergang im Entlueftungssystem von Triebwerkslagerkammern (Pressure Drop and Heat Transfer in the Vent System in an Aero Engine’s Bearing Chamber),” Ph.D. thesis, Logos Verlag, Berlin, Germany) and Flouros (2009, “Analytical and Numerical Simulation of the Two Phase Flow Heat Transfer in the Vent and Scavenge Pipes of the CLEAN Engine Demonstrator,” ASME J. Turbomach., 132(1), p. 011008). Busam has experimentally developed a Nusselt number correlation for an annular flow in a vent pipe. For the heat transfer predictions in scavenge pipes, no particular Nusselt number correlation exist. This paper intends to close the gap in this area. As part of the European Union funded research programme ELUBSYS (Engine Lubrication System Technologies), an attempt was done to simplify the oil system’s architecture. In order to better understand the flow in scavenge pipes, high speed video was taken in two sections of the pipe (vertical and horizontal). In the vertical section, the flow was a wavy annular falling film, whereas the flow in the horizontal section was an unsteady wavy stratified/slug flow. Heat transfer has been investigated in the horizontal section of the scavenge pipe, leaving the investigation on the vertical section for later. Thanks to the provided extensive instrumentation, the thermal field in, on, and around the pipe was recorded, evaluated, and also numerically modeled using ansys cfx version 14. Brand new correlations for two-phase flow heat transfer (Nusselt number) and for pressure drop (friction coefficient) in horizontal scavenge pipes are the result of this work. The Nusselt number correlation has been developed in such a way that smooth transition (i.e., no discontinuity) from two-phase into single phase flow is observed.

BackgroundThe axons of ganglion cells in the nasal retina decussate at the optic chiasm. It is unclear why tumours cause more injury to crossing nasal fibres, thereby giving rise to temporal visual field loss in each eye. To address this issue, the course of fibres through the optic chiasm was examined following injection of a different fluorescent tracer into each eye of a monkey.MethodsUnder general anaesthesia, cholera toxin subunit B—Alexa Fluor 488 was injected into the right eye and cholera toxin subunit B—Alexa Fluor 594 was injected into the left eye of a single normal adult male rhesus monkey. After a week’s survival for anterograde transport, serial coronal sections through the primary optic pathway were examined.ResultsA zone within the core of the anterior and mid portions of the optic chiasm was comprised entirely of crossing fibres. This zone of decussation was delineated by segregated, interwoven sheets of green (right eye) and red (left eye) fibres. It expanded steadily to fill more of the optic chiasm as fibres coursed posteriorly towards the optic tracts. Eventually, crossed fibres became completely intermingled with uncrossed fibres, so that ocular separation was lost.ConclusionsA distinct, central compartment located within the anterior two-thirds of the optic chiasm contains only crossing fibres. Sellar tumours focus their compressive force on this portion of the structure, explaining why they so often produce visual field loss in the temporal fields.

Neuromorphic cognitive computing offers a bio-inspired means to approach the natural intelligence of biological neural systems in silicon integrated circuits. Typically, such circuits either reproduce biophysical neuronal dynamics in great detail as tools for computational neuroscience, or abstract away the biology by simplifying the functional forms of neural computation in large-scale systems for machine intelligence with high integration density and energy efficiency. Here we report a hybrid which offers biophysical realism in the emulation of multi-compartmental neuronal network dynamics at very large scale with high implementation efficiency, and yet with high flexibility in configuring the functional form and the network topology. The integrate-and-fire array transceiver (IFAT) chip emulates the continuous-time analog membrane dynamics of 65 k two-compartment neurons with conductance-based synapses. Fired action potentials are registered as address-event encoded output spikes, while the four types of synapses coupling to each neuron are activated by address-event decoded input spikes for fully reconfigurable synaptic connectivity, facilitating virtual wiring as implemented by routing address-event spikes externally through synaptic routing table. Peak conductance strength of synapse activation specified by the address-event input spans three decades of dynamic range, digitally controlled by pulse width and amplitude modulation (PWAM) of the drive voltage activating the log-domain linear synapse circuit. Two nested levels of micro-pipelining in the IFAT architecture improve both throughput and efficiency of synaptic input. This two-tier micro-pipelining results in a measured sustained peak throughput of 73 Mspikes/s and overall chip-level energy efficiency of 22 pJ/spike. Non-uniformity in digitally encoded synapse strength due to analog mismatch is mitigated through single-point digital offset calibration. Combined with the flexibly layered and recurrent synaptic connectivity provided by hierarchical address-event routing of registered spike events through external memory, the IFAT lends itself to efficient large-scale emulation of general biophysical spiking neural networks, as well as rate-based mapping of rectified linear unit (ReLU) neural activations.

The effective transverse relaxation rate (R2*) is sensitive to the microstructure of the human brain like the g-ratio which characterises the relative myelination of axons. However, the fibre-orientation dependence of R2* degrades its reproducibility and any microstructural derivative measure. To estimate its orientation-independent part (R2,iso*) from single multi-echo gradient-recalled-echo (meGRE) measurements at arbitrary orientations, a second-order polynomial in time model (hereafter M2) can be used. Its linear time-dependent parameter, β1, can be biophysically related to R2,iso* when neglecting the myelin water (MW) signal in the hollow cylinder fibre model (HCFM). Here, we examined the performance of M2 using experimental and simulated data with variable g-ratio and fibre dispersion. We found that the fitted β1 can estimate R2,iso* using meGRE with long maximum-echo time (TEmax ≈ 54 ms), but not accurately captures its microscopic dependence on the g-ratio (error 84%). We proposed a new heuristic expression for β1 that reduced the error to 12% for ex vivo compartmental R2 values. Using the new expression, we could estimate an MW fraction of 0.14 for fibres with negligible dispersion in a fixed human optic chiasm for the ex vivo compartmental R2 values but not for the in vivo values. M2 and the HCFM-based simulations failed to explain the measured R2*-orientation-dependence around the magic angle for a typical in vivo meGRE protocol (with TEmax ≈ 18 ms). In conclusion, further validation and the development of movement-robust in vivo meGRE protocols with TEmax ≈ 54 ms are required before M2 can be used to estimate R2,iso* in subjects.

Equations have been developed to describe cardiac action potentials and pacemaker activity. The model takes account of extensive developments in experimental work since the formulation of the M.N.T. (R. E. McAllister, D. Noble and R. W. Tsien, J. Physiol., Lond. 251, 1-59 (1975)) and B.R. (G. W. Beeler and H. Reuter, J. Physiol., Lond . 268, 177-210 (1977)) equations. The current mechanism i K2 has been replaced by the hyperpolarizing-activated current, i f . Depletion and accumulation of potassium ions in the extracellular space are represented either by partial differential equations for diffusion in cylindrical or spherical preparations or, when such accuracy is not essential, by a three-compartment model in which the extracellular concentration in the intercellular space is uniform. The description of the delayed K current, i K , remains based on the work of D. Noble and R. W. Tsien ( J. Physiol., Lond . 200, 205-231 (1969 a )). The instantaneous inward-rectifier, i K1 , is based on S. Hagiwara and K. Takahashi’s equation ( J. Membrane Biol . 18, 61-80 (1974)) and on the patch clamp studies ofB. Sakmann and G. Trube ( J. Physiol., Lond . 347, 641-658 (1984)) and of Y. Momose, G. Szabo and W. R. Giles ( Biophys. J . 41, 311a (1983)). The equations successfully account for all the properties formerly attributed to i K2 , as well as giving more complete descriptions of i K1 and i K . The sodium current equations are based on experimental data of T. J. Colatsky ( J.Physiol., Lond. 305, 215-234 (1980)) and A. M. Brown, K. S. Lee and T. Powell ( J.Physiol., Lond. , Lond. 318, 479-500 (1981)). The equations correctly reproduce the range and magnitude of the sodium ‘window’ current. The second inward current is based in part on the data of H. Reuter and H. Scholz ( J. Physiol., Lond . 264, 17-47 (1977)) and K. S. Lee and R. W. Tsien ( Nature, Lond . 297,498-501 (1982)) so far as the ion selectivity is concerned. However, the activation and inactivation gating kinetics have been greatly speeded up to reproduce the very much faster currents recorded in recent work. A major consequence of this change is that Ca current inactivation mostly occurs very early in the action potential plateau. The sodium-potassium exchange pump equations are based on data reported by D. C. Gadsby ( Proc. natn. Acad. Sci. U. S. A. 77, 4035-4039 (1980)) and by D. A. Eisner and W. J. Lederer ( J. Physiol., Lond . 303, 441-474 (1980)). The sodium-calcium' exchange current is based on L. J. Mullins’ equations ( J. gen.. Physiol. 70, 681-695 (1977)). Intracellular calcium sequestration is represented by simple equations for uptake into a reticulum store which then reprimes a release store. The repriming equations use the data of W. R. Gibbons & H. A. Fozzard ( J. gen. Physiol . 65, 367-384 (1975 b )). Following Fabiato & Fabiato’s work ( J. Physiol., Lond. 249, 469-495 (I975)), Ca release is assumed to be triggered by intracellular free calcium. The equations reproduce the essential features of intracellular free calcium transients as measured with aequorin. The explanatory range of the model entirely includes and greatly extends that of the M.N.T. equations. Despite the major changes made, the overall time-course of the conductance changes to potassium ions strongly resembles that of the M.N.T. model. There are however important differences in the time courses of Na and Ca conductance changes. The Na conductance now includes a component due to the hyperpolarizing-activated current, i r , which slowly increases during the pacemaker depolarization. The Ca conductance changes are very much faster than in the M.N.T. model so that in action potentials longer than about 50 ms the primary contribution of the fast gated calcium channel to the plateau is due to a steady-state ‘window’ current or non-inactivated component. Slower calcium or Ca-activated currents, such as the Na-Ca exchange current, or Ca-gated currents, or a much slower Ca channel must then play the dynamic role previously attributed to the kinetics of a single type of calcium channel. This feature of the model in turn means that the repolarization process should be related to the inotropic state, as indicated by experimental work. The model successfully reproduces intracellular sodium concentration changes produced by variations in [Na]0, or Na-K pump block. The sodium dependence of the overshoot potential is well reproduced despite the fact that steady state intracellular Na is proportional to extracellular Na, as in the experimental results of D. Ellis J. Physiol., Lond . 274, 211-240 (1977)). The model reproduces the responses to current pulses applied during the plateau and pacemaker phases. In particular, a substantial net decrease in conductance is predicted during the pacemaker depolarization despite the fact that the controlling process is an increase in conductance for the hyperpolarizing-activated current. The immediate effects of changing extracellular [K] are reproduced, including: (i) the shortening of action potential duration and suppression of pacemaker activity at high [K ]; (ii) the increased automaticity at moderately low [K ]; and (iii) the depolarization to the plateau range with premature depolarizations and low voltage oscillations at very low [K]. The ionic currents attributed to changes in Na-K pump activity are well reproduced. It is shown that the apparent K m for K activation of the pump depends strongly on the size of the restricted extracellular space. With a 30% space (as in canine Purkinje fibres) the apparent K m is close to the assumed real value of 1 mM . When the extracellular space is reduced to below 5% , the apparent K m increases by up to an order of magnitude. A substantial part of the pump is then not available for inhibition by low [K] b . These results can explain the apparent discrepancies in the literature concerning the K m for pump activation.