Littérature scientifique sur le sujet « Ionic homeostasi »

Subcellular compartments commonly identified and analyzed by high resolution electron probe x-ray microanalysis (EPXMA) include mitochondria, cytoplasm and endoplasmic or sarcoplasmic reticulum. These organelles and cell regions are of primary importance in regulation of cell ionic homeostasis. Correlative structural-functional studies, based on the static probe method of EPXMA combined with biochemical and electrophysiological techniques, have focused on the role of these organelles, for example, in maintaining cell calcium homeostasis or in control of excitation-contraction coupling. New methods of real time quantitative x-ray imaging permit simultaneous examination of multiple cell compartments, especially those areas for which both membrane transport properties and element content are less well defined, e.g. nuclei including euchromatin and heterochromatin, lysosomes, mucous granules, storage vacuoles, microvilli. Investigations currently in progress have examined the role of Zn-containing polyphosphate vacuoles in the metabolism of Leishmania major, the distribution of Na, K, S and other elements during anoxia in kidney cell nuclel and lysosomes; the content and distribution of S and Ca in mucous granules of cystic fibrosis (CF) nasal epithelia; the uptake of cationic probes by mltochondria in cultured heart ceils; and the junctional sarcoplasmic retlculum (JSR) in frog skeletal muscle.

An inability to regulate ionic and metabolic homeostasis is related to a reduction in the developmental capacity of the embryo. The early embryo soon after fertilisation and up until compaction appears to have a reduced capacity to regulate its homeostasis. The reduced ability to regulate homeostasis, such as intracellular pH and calcium levels, by the precompaction-stage embryo appears to impact on the ability to regulate mitochondrial function and maintain adequate levels of energy production. This reduction in ATP production causes a cascade of events leading to disrupted cellular function and, perhaps ultimately, disrupted epigenetic regulation and aberrant placental and fetal development. In contrast, after compaction the embryo takes on a more somatic cell-like physiology and is better able to regulate its physiology and therefore appears less vulnerable to stress. Therefore, for human IVF it would seem important for the establishment of healthy pregnancies that the embryos are maintained in systems that are designed to minimise homeostatic stress, particularly for the cleavage-stage embryos, as exposure to stress is likely to culminate in impaired embryo function.

Epileptic activity often arises after a latent period following traumatic brain injury. Several factors contribute to the emergence of post-traumatic epilepsy, including disturbances to ionic homeostasis, pathological action of intrinsic and synaptic homeostatic plasticity, and remodeling of anatomical network synaptic connectivity. We simulated a large-scale, biophysically realistic computational model of cortical tissue to study the mechanisms underlying the genesis of post-traumatic paroxysmal epileptic-like activity in the deafferentation model of a severely traumatized cortical network. Post-traumatic generation of paroxysmal events did not require changes of the structural connectivity. Rather, network bursts were induced following the action of homeostatic synaptic plasticity, which selectively influenced functionally dominant groups of intact neurons with preserved inputs. This effect critically depended on the spatial density of intact neurons. Thus in the deafferentation model of post-traumatic epilepsy, a trauma-induced change in functional (rather than anatomical) connectivity might be sufficient for epileptogenesis.

The constant composition of body fluids in insects is maintained by the cooperative interaction of gastrointestinal and urinary tissues. Water follows ionic movements, which are driven by the basolateral Na+/K+-ATPase and/or the apical 'K+(or Na+) pump'. The latter now is thought to be the functional expression of a parallel arrangement of a proton-motive V-ATPase and a K+(or Na+)/nH+ antiport. This review focuses on the pathways for the movement of monovalent inorganic ions through epithelia involved in ion homeostasis. A graphical summary compares the principal findings with respect to cation secretion in lepidopteran caterpillar midgut goblet cells (K+) and in brush-border cells of Malpighian tubules (K+, Na+).

With the global population predicted to grow by at least 25% by 2050, the need for sustainable production of nutritious foods is important for human and environmental health. Recent progress demonstrate that membrane transporters can be used to improve yields of staple crops, increase nutrient content and resistance to key stresses, including salinity, which in turn could expand available arable land. Exposure to salt stress affects plant water relations and creates ionic stress in the form of the cellular accumulation of Na+ and Cl- ions. However, salt stress also impacts heavily on the homeostasis of other ions such as Ca2+, K+, and NO3- and therefore requires insights into how transport and compartmentation of these nutrients are altered during salinity stress. Since Na+ interferes with K+ homeostasis, maintaining a balanced cytosolic Na+/K+ ratio has become a key salinity tolerance mechanism. Achieving this homeostatic balance requires the activity of Na+ and K+ transporters and/or channels. The aim of this review is to seek answers to this question by examining the role of major ions transporters and channels in ions uptake, translocation and intracellular homeostasis in plants.

Electrophysiological and structural disruptions in cardiac arrhythmias are closely related to mitochondrial dysfunction. Mitochondria are an organelle generating ATP, thereby satisfying the energy demand of the incessant electrical activity in the heart. In arrhythmias, the homeostatic supply–demand relationship is impaired, which is often accompanied by progressive mitochondrial dysfunction leading to reduced ATP production and elevated reactive oxidative species generation. Furthermore, ion homeostasis, membrane excitability, and cardiac structure can be disrupted through pathological changes in gap junctions and inflammatory signaling, which results in impaired cardiac electrical homeostasis. Herein, we review the electrical and molecular mechanisms of cardiac arrhythmias, with a particular focus on mitochondrial dysfunction in ionic regulation and gap junction action. We provide an update on inherited and acquired mitochondrial dysfunction to explore the pathophysiology of different types of arrhythmias. In addition, we highlight the role of mitochondria in bradyarrhythmia, including sinus node dysfunction and atrioventricular node dysfunction. Finally, we discuss how confounding factors, such as aging, gut microbiome, cardiac reperfusion injury, and electrical stimulation, modulate mitochondrial function and cause tachyarrhythmia.

Work from our group and other laboratories showed that the nucleus could be considered as a cell within a cell. This is based on growing evidence of the presence and role of nuclear membrane G-protein coupled receptors and ionic transporters in the nuclear membranes of many cell types, including vascular endothelial cells, endocardial endothelial cells, vascular smooth muscle cells, cardiomyocytes, and hepatocytes. The nuclear membrane receptors were found to modulate the functioning of ionic transporters at the nuclear level, and thus contribute to regulation of nuclear ionic homeostasis. Nuclear membranes of the mentioned types of cells possess the same ionic transporters; however, the type of receptors is cell-type dependent. Regulation of cytosolic and nuclear ionic homeostasis was found to be dependent upon a tight crosstalk between receptors and ionic transporters of the plasma membranes and those of the nuclear membrane. This crosstalk seems to be the basis for excitation–contraction coupling, excitation–secretion coupling, and excitation – gene expression coupling. Further advancement in this field will certainly shed light on the role of nuclear membrane receptors and transporters in health and disease. This will in turn enable the successful design of a new class of drugs that specifically target such highly vital nuclear receptors and ionic transporters.

Neurotoxicity is defined as “an adverse change in the structure or function of the nervous system that results from exposure to a chemical, biological or physical agent". lonic channels, transporters, receptors for neurotransmitters and neurohormones are the main modulators of neuronal activity. It is therefore to be expected that the interfering with these proteins induces significant and potentially damaging effects in these tightly regulated and highly responsive cells. The present research project has been focused on the study of the role of specific ionic channels and the main mechanisms involved regarding two cases of neurotoxicity, which were widely documented but not completely understood: 1) the potential neurotoxicity induced by SiO2 NP and 2) the one induced by OHP. This issue has been addressed by means of an integrated approach that combine electrophysiological recordings both at single cell level by using the patch clamp technique, and at population level by using multielectrode arrays (MEAs), as well as quantitative real-time polymerase chain reaction (qRT-PCR) and/or RNAseq for a trascriptome screening. Members of TRP channel family (TRPA1, TRPV1, TRPV4), two pore domain K+ (K2P) channel family, as well as connexins and pannexin-like channels, are the major components of the responses by SiO2 NP and OHP. In conclusion, the information presented here may be valuable, particularly for contributing to current knowledge on this subject mainly regarding cells of the nervous system, as some evidence and mechanistic suggestions are provided.

Epilepsy is not a single disorder, but presents with a surrounding of symptoms that are not always of immediate identification and classification. About 50 million people worldwide have epilepsy. Seizures are more likely to occur in young children, or people over the age of 65 years. The mainstay of treatment of epilepsy is preventive anticonvulsant medication with anti epileptic drugs (AED). Despite the proven efficacy of most of these drugs, it is estimated that over 30% of people with epilepsy do not reach complete seizure control, and this category of patients is eligible for surgical therapy. Among them, people suffering from focal seizure and in particular temporal lobe epilepsy are candidates for surgery. In recent years, surgical ablation of the epileptogenic focus has been rewarded as the best way to cure seizures in patients with intractable focal epilepsy. Diagnostic scalp and intracranial stereo-EEG recordings can provide direct information from the epileptogenic focus and surrounding areas in order to circumscribe the zone to be surgically removed. Data obtained from the analysis of the patients' EEG brought to the identification of specific ictal patterns which in turn helped to better classify the already clinically defined seizure types. These patterns can be reproduced in animal models of epilepsy and/or seizures. Focal seizures in the temporal lobe of the isolated in vitro guinea pig brain can be induced by perfusion of proconvulsant drugs. The electrophysiological recordings from the limbic structures of this animal model inform about the mechanisms leading to seizure onset (ictogenesis) and their progression. These phenomena are being studied both from a neuro-physiological and functional point of view; also histology and other anatomo-functional techniques give us a global idea of the activities occurring in different brain compartments during seizure-like events. The ultimate goal of this research will be to further clarify the causes for which a focal seizure is generated and the regulatory mechanisms that govern the different patterns similar to those identified in humans. Intracellular recordings from principal neurons in the superficial and deep layers of the entorhinal cortex showed a different involvement of these two regions in seizure initiation and development. We demonstrate that at seizure onset there is a strong activation of GABAergic interneuron (Gnatkovsky et al., 2008). This finding points to a primary role of GABAergic inhibition in seizure generation. We further showed that slow potentials recorded during the first steps of ictal activity are a typical sign of modifications of ionic composition of the extracellular medium and describe very well the shape of low voltage shifts with fast activity (Trombin et al., in preparation). Spikes shape identified by intracellular recordings during seizures was also analyzed to evaluate the epileptogenic network. The correlation of AP changes during seizures with the field potential and the increase in extracellular [K] clearly indicates both neuronal and non-neuronal processes, take place during the initiation and the termination of a seizure (Trombin et al, in preparation). Taken together all these data point out a multi-factorial scenario in which inhibitory networks play a crucial role in seizure generation, in association with changes in glial function and extracellular homeostasis. The impairment of one of these elements can be a triggering event in the development of seizures (ictogenesis), and can start in turn a cascade of permanent modifications that maintain an hyper-excitability condition, leading to epileptogenesis. The precise knowledge of each passage needed to transform a normal tissue into an epileptogenic one is a fundamental achievement in order to recognize and classify the different syndromic manifestations of epilepsy. Further, the possibility to interfere with one of the above mentioned processes is of evident relevance for the modulation of seizure beginning and establishment.

Chloroplasts and mitochondria play essential roles in the plant physiology and are emerging as important players in intracellular Ca2+ signaling. A major role in the context of organellar ion homeostasis is played by ion channels. In fact, they are responsible for the regulation of ion distribution between compartments and they are proposed to guarantee Ca2+ signaling, proper osmotic potential, optimal pH for enzymatic activities and electron transport chains’ function. In plants, only a few of channel families have been found to localize to chloroplast/mitochondria and most of them have not been fully characterized. In addition, the molecular mechanisms by which chloroplasts and mitochondria accumulate and release Ca2+ are still far from being clarified. The present work aimed to characterize possible players in organellar Ca2+ flux-mediating systems in plants, namely the Ionotropic Glutamate Receptors (GLRs, non-selective cation channels) and Mitochondrial Calcium Uniporters (MCUs), combining reverse genetics, biochemistry and in vivo localization studies. The research here presented allowed to deepen the study on land plant GLRs, to characterize two novel organellar channels of A. thaliana, i. e. AtGLR3.5 and AtMCU, and to lay the ground for the characterization of the Physcomitrella patens GLRS, PpGLRs, from different points of view. Results revealed additional variability of GLRs among photosynthetic organisms and support the role of GLRs in the regulation of various organellar processes such as photoprotective mechanisms, senescence and mitochondrial structure integrity maintenance. Importantly, the characterization of AtGLR3.5 provided the molecular identification of the first cation channel in plant mitochondria and the characterization of AtMCU1 and MICU allowed for the first time the proposal of a model for the existence and regulation of Ca2+ fluxes in plant mitochondria via MCU complex. The present work therefore contributed to add new knowledge to the field of the regulation of ion homeostasis, especially Ca2+ homeostasis, in mitochondria and chloroplasts.
Cloroplasti e mitocondri hanno un ruolo fondamentale nella fisiologia vegetale e stanno emergendo come importanti attori nel signaling del Ca2+ intracellulare. Un ruolo fondamentale nel contesto dell’omeostasi ionica organellare è giocato dai canali ionici. Infatti essi sono responsabili della regolazione della distribuzione ionica fra compartimenti ed è stato proposto che contribuiscano a garantire il signaling del Ca2+, l’appropriato potenziale osmotico, il pH ottimale per le attività enzimatiche e il funzionamento delle catene di trasporto elettronico. Nelle piante, solo poche famiglie di canali sono state identificate in cloroplasti/mitocondri e la maggior parte di loro non è stata pienamente caratterizzata. Inoltre, il meccanismo molecolare attraverso cui cloroplasti e mitocondri accumulano e rilasciano Ca2+ è ancora lontano dall’essere chiarito. Lo scopo del presente lavoro è stato quello di caratterizzare possibili attori coinvolti nel nella mediazione dei flussi di Ca2+ organellari, in particolare i recettori ionotropici del glutammato (GLRs) e gli uniporti mitocondriali del calcio (MCU), combinando tecniche di genetica inversa, biochimica e studi di localizzazione in vivo. La ricerca qui presentata ha permesso di approfondire lo studio sui GLR vegetali, di caratterizzare due nuovi canali organellari di A. thaliana, AtGLR3.5 e AtMCU, e di gettare le fondamenta per la caratterizzazione dei GLR di Physcomitrella patens, PpGLR, da diversi punti di vista. I risultati del lavoro hanno rivelato ulteriore variabilità dei GLR fra gli organismi fotosintetici e hanno mostrato come i GLR siano coinvolti nella regolazione di diversi processi organellari come i meccanismi di fotoprotezione, la senescenza e il mantenimento dell’integrità strutturale mitocondriale. La caratterizzazione di AtGLR3.5 ha permesso l’identificazione molecolare del primo canale cationico mitocondriale vegetale e la caratterizzazione di AtMCU1 ha permesso per la prima volta di proporre un modello che preveda l’esistenza e la regolazione dei flussi di Ca2+ nei mitocondri vegetali per mezzo del complesso MCU. Il lavoro qui presentato ha pertanto contribuito ad aggiungere nuova conoscenza al campo della regolazione dell’omeostasi ionica, specialmente l’omeostasi del Ca2+, nei mitocondri e nei cloroplasti.

Muscle contractions induce cellular potassium (K+) efflux which may contribute to impaired muscle cell membrane excitability and fatigue. The magnitude of K+ changes are dependent on the size of contracting muscle mass, duration and intensity of exercise, and health and fitness status of participants. Activation of the sarcolemmal and t-tubular bound sodium-potassium adenosine 5’ triphosphatase enzyme (Na+,K+ATPase, NKA) mediates muscle cell K+ and Na+ active exchange, and is instrumental in the maintenance of muscle cellular and plasma K+ homeostasis during exercise. Therefore modulations of NKA function might enhance or impair exercise induced K+ disturbances, and theoretically can have a profound effect on muscle excitability and exercise performance. This thesis examined the effects of two interventions designed to induce acute or short term upregulation and downregulation of NKA activity on K+ homeostasis and exercise performance in healthy humans. Study 1 investigated the effects of metabolically induced alkalosis on plasma K+ regulation during submaximal finger flexion (small muscle mass) contractions and fatigue in healthy humans. Study 2 investigated the effects of a clinically relevant dose of digoxin administration on K+ regulation, during intermittent supramaximal finger flexion contractions (small muscle mass) and fatigue in healthy humans. Study 3 investigated the effects of digoxin on K+ regulation during progressive increasing intensity submaximal leg cycling exercise (large muscle mass) and fatigue in the same healthy participants as in study 2. A secondary focus of this thesis was to examine the ionic, metabolic and acid-base disturbances during small and large muscle mass exercise and in recovery. This included the regulatory role of NKA in active (study 1 and 2) and inactive tissue (study 3), during small (study 1 and 2) and large (study 3) muscle mass exercise.

Alongside with the drought, soil salinity is one the major environmental constraints that reduces crop growth and yield worldwide. According to recent reports, salinity stress is costing agricultural sector over US $27.3 billion per annum in lost revenues; which also aggravates the global food security. Improving salinity tolerance is a challenging task that requires understanding key physiological traits in naturally salt tolerant plant species. Halophytes are salt loving plants and they have very diverse array of physiological and biochemical mechanisms to encounter salinity stress. Therefore, understanding the fine-print of salinity-induced constraints on plant growth and/or salinity tolerance mechanisms in salt-tolerant halophytes is of a key importance for enhancing salinity stress tolerance in salt sensitive crop plants. The extent of salinity tolerance depends considerably on crop species and families. Thus, comparing different plant species from the same family or genus can provide much better understanding of physiological mechanisms conferring differential salinity tolerance. In this work, we have selected Chenopodiaceae family, one of most important subfamilies of Amaranthaceae family that contains numerous plant species, including halophtytic (e.g. Chenopodium quinoa, Chenopodium album, Atriplex lentiformis) and glycophytic species (e.g. Spinacia oleracea (spinach). Amongst different plant species, we have selected Chenopodium quinoa (quinoa hereafter) as a dicotyledonous halophytic plant species and Spinacia oleracea (spinach hereafter) as glycophytic plants species. Some previous and basic reports showed that Chenopodiaceae family showed a considerable intra- and inter-specific variation at the whole plant level under saline conditions. However, to the best of our knowledge, no much specific details on the cellular mechanisms conferring this intra- and inter-specific variability in the context of salinity tolerance are available in the literature. Salinity stress is very complex abiotic stress that induces cytosolic toxicity and oxidative damage by causing ROS production. Under saline conditions, the production of different ROS such as hydrogen peroxide (H\(_2\)O\(_2\)), superoxide radical (O\(_2\)\(^-\)) and hydroxyl radical (•OH) at different sites in cells causes significant damages to nucleic acids, proteins, and lipids. Elevated ROS levels also cause major disturbance to plant ionic homeostasis. At the same time, at low concentrations ROS can act as signalling molecules to control various physiological processes such as cell growth, pollen development, hormonal control, stress signalling and transduction, and ion transport across the plasma membrane. Until now very few studies have been published showing the role of different types of ROS in regulating ion transport at tissue levels. Therefore, in order to understand above tissue specific and intra- and inter-specific variability in salinity tolerance, set of physiological, electrophysiological and confocal imaging experiments were conducted to answer some of these specific questions: I. How does K\(^+\) retention pattern (a key determinant of the salinity tissue tolerance mechanism) in different tissues (root and leaf mesophyll) differ between halophyte and glycophyte species? II. Can plants (especially halophytic plants) employ other ROS such as •OH and O\(_2\)\(^-\) to shape Ca\(^{2+}\) flux signatures? III. Is there any specific Ca\(^{2+}\) or ROS signatures involved in early salt sensing in halophytes? IV. How do halophytes avoid Na\(^+\) cytosolic toxicity and enhance K\(^+\) retention ability? V. How can halophytes retain more K\(^+\)? Do they spend much energy (H\(^+\)-ATPase activity) to retain K\(^+\) as compared with spinach? VI. What could be possible players behind reduced K\(^+\)-efflux from leaf mesophyll and roots in quinoa in relation to acclimation? This work showed that salinity application arrested plant growth in a highly tissue- and treatment-specific manner and was more severe in glycophytic spinach plants however quinoa was able to withstand salinity stress and produced relative higher plant biomass even at sea level saline conditions (500mM NaCl). Analysis of shoot and xylem sap Na\(^+\) and K\(^+\) contents have revealed the key factor determining differential salinity tolerance between quinoa and spinach species was shoot K\(^+\) (not Na\(^+\)) content and kinetics of xylem ion loading suggested that quinoa species actively load and used Na\(^+\) for osmotic adjustment in shoot to avoid energy expensive synthesis of organic osmolytes. To further gain insight into such whole-plant observations, kinetics of K\(^+\), H\(^+\), Ca\(^{2+}\) flux responses from leaf mesophyll in were measured using non-invasive ion flux measuring MIFE technique in response to salinity stress and H\(_2\)O\(_2\) stress. Moreover, laser microscope confocal imaging technique was used to measure the cytosolic and vacuolar intensities of the fluorescent signals of K\(^+\), Na\(^+\) and Ca\(^{2+}\) from different root zones in response to salinity stress and H\(_2\)O\(_2\)2 stress. It was also observed that mesophyll cells in glycophytic spinach lost 2 to 6-fold more K\(^+\) compared with its halophytic quinoa counterpart. Treatment with NaCl resulted in significant increase in a transient H\(^+\)-efflux in the leaf mesophyll in spinach, suggesting that spinach spent more ATP to up-regulate H\(^+\)-ATPase activity while quinoa avoid this mechanism to use same energy in defence system, consistent with recently suggested concept of the 'metabolic switch‘. Among root zones, NaCl- and ROS- induced K\(^+\)-efflux was more pronounced in the root apex while mature zone showed relatively higher K\(^+\) retention, especially in quinoa. This differential sensitivity between different root zones was specifically originated from a 10-folds difference in K\(^+\)-efflux between the mature zone and the apical region (much poorer in the root apex) of the root. Three factors behind this poor K\(^+\) retention ability were: (1) an intrinsically lower H\(^+\)-ATPase activity in the root apex; (2) greater salt-induced membrane depolarization and (3) a higher ROS production under NaCl and a larger density of ROS-activated cation currents in root. Moreover ROS (H\(_2\)O\(_2\)) production was increased with time in all root zones in both species and accompanied with cytosolic Ca\(^{2+}\) elevation in quinoa, suggesting that quinoa (halophytic species) used ROS as a signalling moiety in stress adaptation. Elevation in cytosolic Ca\(^{2+}\) reduced cytosolic Na\(^+\), possibly by SOS1 pathway. Both species showed tremendous K\(^+\)-efflux in response to •OH and O\(_2\)\(^-\) radical but Ca\(^{2+}\)\) flux patterns revealed different results. In response to O\(_2\)\(^-\), a net Ca\(^{2+}\)-efflux was observed while in response to •OH, a net Ca\(^{2+}\)-influx was noted, suggesting halophytes may use ROS specific Ca\(^{2+}\) signatures to activate stress adaptation process. Moreover, halophytes (or at least quinoa) may use Ca\(^{2+}\)-efflux system to restore basal cytosolic Ca\(^{2+}\) level upon O\(_2\)\(^-\) treatment. Under long term salinity conditions, quinoa grown under higher NaCl level (300mM NaCl) showed much reduced responses to external H\(_2\)O\(_2\), suggesting desensitization of K\(^+\)-permeable ion channels to ROS. Moreover, quinoa showed strongest Ca\(^{2+}\) flux response to H\(_2\)O\(_2\) during acclimation, suggesting the important role of ROS-induced cytosolic Ca\(^{2+}\) elevation in stress signalling and adaptive cascade. Spinach was less efficient in doing so, thus showed massive K\(^+\)-efflux and reduced K\(^+\) retention ability. In conclusion, results from current work showed that NaCl and ROS stress induced massive K\(^+\)\(^+\) loss. This loss was highly tissue-specific and more pronounced in glycophytic spinach plants. Several mechanisms were highlighted in this work behind such response in quinoa (i) higher vacuolar Na\(^+\) sequestration ability in roots, thus reduced Na\(^+\) cytosolic toxicity. (ii) It can employ H\(_2\)O\(_2\) to activate stress signalling cascades, (iii) higher K\(^+\) retention in leaf mesophyll was strongly correlated with plant biomass, SPAD and stomatal conductance, (iv) The results obtained indicated a major difference in distribution of energy between "metabolic" and "defence" pools. Future research should focus on the difference and mechanisms of the regulation of H\(^+\)-ATPase activity between halophytes and glycophytes, and the role of ROS in this process, (V) during acclimation, quinoa showed relatively more Na\(^+\) accumulation (based on coroNa green fluorescence signal) than spinach. Thus, it will be of a significant importance to reveal the contribution of numerous components (e.g. tonoplastic NHX, or FV/SV channels) towards vacuolar Na\(^+\) sequestration. One of most important discoveries in this study was the identification of the electrophysiological role of ROS specific Ca\(^{2+}\) signatures in the regulation of K\(^+\) homeostasis and stress adaptation. The use of some techniques such patch clamp and CRISPR/CAS 9 will help to reveal the molecular identity of different ion transporters in quinoa and spinach in response to different ROS especially to •OH and O\(_2\)\(^-\) radical at transcriptional and post transcriptional levels, to further understand the molecular basis of the observed physiological salinity tolerance mechanisms.

Waterlogging is a serious environmental threat worldwide that severely limits agricultural production. Waterlogging stress adversely affects 10% of the global land area and annual financial losses to agricultural crop production are estimated to exceed €60 billion. Many regions of the world (e.g. Australia, China) are regularly affected by waterlogging stress. Barley ranks fifth amongst all crops in dry matter production in the world. In Australia, most of the barley cultivars are waterlogging sensitive. In most cases, plants are grown on duplex soil, which has a layer of sandy soil over a comparatively water-resistant base of clay soil. Therefore, the continued rainfall events can lead to increasing water tables in the root zone. Waterlogging is a complex trait that conferred by several physiological and biochemical mechanisms. While the major attention of plant breeders was on traits related to oxygen supply and retention (radial oxygen loss; aerenchyma formation; etc), traits related to plant’s ability to maintain ionic homeostasis under waterlogged conditions received much less attention. Therefore, the main objectives of this study were (1) to investigate the effects of oxygen deprivation on intracellular K\(^+\) signalling and homeostasis, and its potential roles in acclimation to oxygen-deprived conditions in barley; (2) to develop reliable screening protocols for evaluation of some key physiological traits conferring waterlogging stress tolerance which can be used in breeding programs; (3) to link waterlogging tolerance with K\(^+\) retention, membrane potential maintenance and ROS stress tolerance by using a QTL approach; (4) to link these traits with other abiotic stresses such as salinity in order to make the deep understanding of tolerance mechanisms in barley. The major constraint that plants undergo in waterlogged conditions is the inadequate supply of oxygen to submerged parts. Oxygen depletion under waterlogged conditions results in a compromised operation of H\(^+\) -ATPase, with strong implications for membrane potential maintenance, excessive ROS accumulation, cytosolic pH homeostasis, and transport of major nutrients across membranes. The above effects, however, are highly tissue-specific and time-dependent, and the causal link between hypoxia-induced changes to cell’s ionome and plant adaptive responses to hypoxia is not well established. This work aimed to fill the above gap and investigate the effects of oxygen deprivation on K\(^+\) signalling and homeostasis in plants and potential roles of GORK (depolarization-activated outward-rectifying potassium) channels in plant adaptation to oxygen-deprived conditions in barley. The significant K\(^+\) loss was observed in roots exposed to hypoxic conditions; this loss correlated with the cell’s viability. The stress-induced K\(^+\) loss was stronger in the root apex immediately after stress onset but became more pronounced in the root base as the stress progressed. The amount ofK\(^+\) in shoots of plants grown in waterlogged soil correlated strongly with K\(^+\) flux under hypoxia measured in laboratory experiments. Hypoxia-induced membrane depolarization was less pronounced in the tolerant group of cultivars. The expression of GORK was down-regulated by 1.5-fold in mature root while upregulated by 10-fold in the apex after 48 h hypoxia stress. Taken together, our results suggest that GORK channel plays a central role in K\(^+\) retention and signalling under hypoxia stress and measuring hypoxia-induced K\(^+\) fluxes from the mature root zone may be used as a physiological marker to select waterlogging tolerant varieties in breeding programs. Waterlogging and salinity are two major abiotic stresses that could occur simultaneously and hamper crop production world-wide resulting in multibillion losses. Plant abiotic stress tolerance is conferred by many interrelated mechanisms. Amongst these, the cell’s ability to maintain membrane potential is considered to be amongst the most crucial traits, a positive relationship between the ability of plants to maintain highly negative membrane potential and its tolerance to both salinity and waterlogging stress. However, no attempts have been made to identify quantitative trait loci (QTL) conferring this trait. In this study, the microelectrode MIFE technique was used to measure the plasma membrane potential of epidermal root cells of 150 double haploid (DH) lines of barley (Hordeum vulgare L.) from a cross between a Chinese landrace TX9425 and Japanese malting cultivar Naso Nijo under hypoxic conditions. A major QTL for the membrane potential in the epidermal root cells in hypoxia-exposed plants was identified. This QTL was located on 2H, at a similar position to the QTL for waterlogging and salinity tolerance reported in previous studies. Further analysis confirmed that membrane potential showed a significant contribution to both waterlogging and salinity tolerance. The fact that the QTL for membrane potential was controlled by a single major QTL illustrates the power of the single-cell phenotyping approach and opens prospects for fine mapping this QTL. A reduced concentration of oxygen in waterlogged soils leads to oxygen deficiency in plant tissues, resulting in an excessive accumulation of ROS in plants. This ROS accumulation under waterlogged conditions also contributes to limit agricultural production in low-lying rainfed areas worldwide. To identify QTL for ROS tolerance in barley, 187 double haploid (DH) lines from a cross between TX9425 and Naso Nijo were screened for superoxide anion (O\(_2\)\(^{·−}\)) and hydrogen peroxide (H\(_2\)O\(_2\)) accumulated under hypoxia stress. In our experiment, we showed that quantifying ROS contents after 48 h hypoxia could be a fast and reliable approach for the selection of waterlogging tolerant barley genotypes. A major QTL on chromosome 2H was identified for both O\(_2\)\(^{·−}\) (QSO.TxNn.2H) and H\(_2\)O\(_2\) (QHP.TxNn.2H) contents. This QTL was located at the same position as the QTL for the overall waterlogging and salt tolerance reported in previous studies, explaining 23% and 24% of the phenotypic variation, for O\(_2\)\(^{·−}\) and H\(_2\)O\(_2\) contents, respectively. The analysis also showed a causal association between ROS production and both waterlogging and salt stress tolerance. The markers associated with this QTL could potentially be used in future breeding programs to improve waterlogging and salinity tolerance. Taken together, the results of this work showed that hypoxic conditions caused a significant loss of K\(^+\), in a time- and genotype-specific manner. This has affected cell viability and overall plant tolerance. The genotypic difference in waterlogging stress tolerance in barley was conferred by the differential ability to regulate voltage-gated K\(^+\)-permeable channels (GORK) in the mature root epidermis. A strong positive correlation between the ability of mature zone cells to retain K\(^+\) and the overall waterlogging stress tolerance was found, making it possible to recommend using this method as a physiological marker for breeding plants for waterlogging stress tolerance. A major QTL for membrane potential maintenance under hypoxia stress was identified on chromosome 2H using cell-based phenotyping involving microelectrode MIFE technique. Another important finding of this work is the identification of two major QTL for both O\(_2\)\(^{·−}\) and H\(_2\)O\(_2\) accumulation for hypoxia on Chromosome 2H. Interestingly, the QTL for membrane potential and ROS is located at a similar position to that for waterlogging and salinity tolerance on chromosome 2H. The fact that these QTL are detected at a similar position of chromosome 2H indicates a specific mechanism for different stress tolerances including waterlogging and salinity tolerance. Future work should be focusing to fine map these QTL and use this gene in pyramiding different tolerance mechanisms in breeding programs.

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Cortical spreading depression (CSD) is a temporary disruption of local ionic homeostasis that propagates slowly across the cerebral cortex. Cortical spreading depression promotes lesion progression in experimental stroke, and may contribute to the initiation of migraine attacks. The purpose of this study was to investigate the roles of the marked increase of nitric oxide (NO) formation that occurs with CSD. Microdialysis electrodes were implanted in the cortex of anesthetized rats to perform the following operations within the same region: (1) elicitation of CSD by perfusion of high K+ medium; (2) recording of CSD elicitation; (3) application of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME); and (4) recording of dialysate pH changes. The primary effect of L-NAME (0.3 to 3.0 mmol/L in the perfusion medium) was a marked widening of individual CSD wave, resulting essentially from a delayed initiation of the repolarization phase. This change was due to NO synthase inhibition because it was not observed with the inactive isomer D-NAME, and was reversed by L-arginine. This effect did not appear to be linked to the suppression of a sustained, NO-mediated vascular change associated with the superposition of NO synthase inhibition on high levels of extracellular K+. The delayed initiation of repolarization with local NO synthase inhibition may reflect the suppression of NO-mediated negative feedback mechanisms acting on neuronal or glial processes involved in CSD genesis. However, the possible abrogation of a very brief, NO-mediated vascular change associated with the early phase of CSD cannot be ruled out.

AbstractChondrocytes produce the extracellular cartilage matrix required for smooth joint mobility. As cartilage is not vascularised, and chondrocytes are not innervated by the nervous system, chondrocytes are therefore generally considered non-excitable. However, chondrocytes do express a range of ion channels, ion pumps, and receptors involved in cell homeostasis and cartilage maintenance. Dysfunction in these ion channels and pumps has been linked to degenerative disorders such as arthritis. Because the electrophysiological properties of chondrocytes are difficult to measure experimentally, mathematical modelling can instead be used to investigate the regulation of ionic currents. Such models can provide insight into the finely tuned parameters underlying fluctuations in membrane potential and cell behaviour in healthy and pathological conditions. Here, we introduce an open-source, intuitive, and extendable mathematical model of chondrocyte electrophysiology, implementing key proteins involved in regulating the membrane potential. Because of the inherent biological variability of cells and their physiological ranges of ionic concentrations, we describe a population of models that provides a robust computational representation of the biological data. This permits parameter variability in a manner mimicking biological variation, and we present a selection of parameter sets that suitably represent experimental data. Our mathematical model can be used to efficiently investigate the ionic currents underlying chondrocyte behaviour.