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Release Channels (release + channel)

Distribution by Scientific Domains

Life Sciences	62%
Medical Sciences	31%

Selected Abstracts

Screening for the calstabin-ryanodine receptor complex stabilizers JTV-519 and S-107 in doping control analysis

DRUG TESTING AND ANALYSIS, Issue 1 2009
Mario Thevis
Abstract Recent studies outlined the influence of exercise on the stability of the skeletal muscle calstabin1-ryanodine receptor1-complex, which represents a major Ca2+ release channel. The progressive modification of the type-1 skeletal muscle ryanodine receptor (RyR1) combined with reduced levels of calstabin1 and phosphodiesterase PDE4D3 resulted in a Ca2+ leak that has been a suggested cause of muscle damage and impaired exercise capacity. The use of 1,4-benzothiazepine derivatives such as the drug candidates JTV-519 and S-107 enhanced rebinding of calstabin1 to RyR1 and resulted in significantly improved skeletal muscle function and exercise performance in rodents. Due to the fact that the mechanism of RyR1 remodelling under exercise conditions were proven to be similar in mice and humans, a comparable effect of JTV-519 and S-107 on trained athletes is expected, making the compounds relevant for doping controls. After synthesis of JTV-519, S-107, and a putative desmethylated metabolite of S-107, target compounds were characterized using nuclear magnetic resonance spectroscopy and electrospray ionization (ESI),high-resolution/high-accuracy Orbitrap mass spectrometry. Collision-induced dissociation pathways were suggested based on the determination of elemental compositions of product ions and H/D-exchange experiments. The most diagnostic product ion of JTV-519 was found at m/z 188 (representing the 4-benzyl-1-methyl piperidine residue), and S-107 as well as its desmethylated analog yielded characteristic fragments at m/z 153 and 138 (accounting for 1-methoxy-4-methylsulfanyl-benzene and 4-methoxy-benzenethiol residues, respectively). The analytes were implemented in existing doping control screening procedures based on liquid chromatography, multiple reaction monitoring and simultaneous precursor ion scanning modes using a triple quadrupole mass spectrometer. Validation items such as specificity, recovery (68,92%), lower limit of detection (0.1,0.2 ng/mL), intraday (5.2,18.5%) and interday (8.7,18.8%) precision as well as ion suppression/enhancement effects were determined. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Cardiac Calsequestrin: The New Kid on the Block in Arrhythmias

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2009
NAGESH CHOPRA M.D.
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare inherited disease characterized by physical or emotional stress-induced ventricular arrhythmias in the absence of any structural heart disease or QT prolongation. Thus far, mutations in genes encoding the sarcoplasmic reticulum Ca2+ release channel (RYR2) and the sarcoplasmic reticulum Ca2+ binding protein cardiac calsequestrin (CASQ2) have been identified in CPVT patients. Here, we review the role of cardiac calsequestrin in health and disease, with a particular focus on how calsequestrin deficiency can cause arrhythmia susceptibility. Clinical implications and a promising new drug therapy for CPVT are discussed. [source]

Junctin and the histidine-rich Ca2+ binding protein: potential roles in heart failure and arrhythmogenesis

THE JOURNAL OF PHYSIOLOGY, Issue 13 2009
Tracy J. Pritchard
Contractile dysfunction and ventricular arrhythmias associated with heart failure have been attributed to aberrant sarcoplasmic reticulum (SR) Ca2+ cycling. The study of junctin (JCN) and histidine-rich Ca2+ binding protein (HRC) becomes of particular importance since these proteins have been shown to be critical regulators of Ca2+ cycling. Specifically, JCN is a SR membrane protein, which is part of the SR Ca2+ release quaternary structure that also includes the ryanodine receptor, triadin and calsequestrin. Functionally, JCN serves as a bridge between calsequestrin and the Ca2+ release channel, ryanodine receptor. HRC is a SR luminal Ca2+ binding protein known to associate with both triadin and the sarcoplasmic reticulum Ca2+ -ATPase, and may thus mediate the crosstalk between SR Ca2+ uptake and release. Indeed, evidence from genetic models of JCN and HRC indicate that they are important in cardiophysiology as alterations in these proteins affect SR Ca2+ handling and cardiac function. In addition, downregulation of JCN and HRC may contribute to Ca2+ cycling perturbations manifest in the failing heart, where their protein levels are significantly reduced. This review examines the roles of JCN and HRC in SR Ca2+ cycling and their potential significance in heart failure. [source]

Effect of ADP on slow-twitch muscle fibres of the rat: implications for muscle fatigue

THE JOURNAL OF PHYSIOLOGY, Issue 1 2006
W. A. Macdonald
Slow-twitch mechanically skinned fibres from rat soleus muscle were bathed in solutions mimicking the myoplasmic environment but containing different [ADP] (0.1 ,m to 1.0 mm). The effect of ADP on sarcoplasmic reticulum (SR) Ca2+ -content was determined from the magnitude of caffeine-induced force responses, while temporal changes in SR Ca2+ -content allowed determination of the effective rates of the SR Ca2+ -pump and of the SR Ca2+ -leak. The SR Ca2+ -pump rate, estimated at pCa (,log10[Ca2+]) 7.8, was reduced by 20% as the [ADP] was increased from 0.1 to 40 ,m, with no further alteration when the [ADP] was increased to 1.0 mm. The SR Ca2+ -leak rate constant was not altered by increasing [ADP] from 0.1 to 40 ,m, but was increased by 26% when the [ADP] was elevated to 1.0 mm. This ADP-induced SR Ca2+ -leak was insensitive to ruthenium red but was abolished by 2,5-di(tert-butyl)-1,4-hydroquinone (TBQ), indicating that the leak pathway is via the SR Ca2+ -pump and not the SR Ca2+ -release channel. The decrease in SR Ca2+ -pump rate and SR Ca2+ -leak rate when [ADP] was increased led to a 40% decrease in SR Ca2+ -loading capacity. Elevation of [ADP] had only minor direct effects on the contractile apparatus of slow-twitch fibres. These results suggest that ADP has only limited depressing effects on the contractility of slow-twitch muscle fibres. This is in contrast to the marked effects of ADP on force responses in fast-twitch muscle fibres and may contribute to the fatigue-resistant nature of slow-twitch muscle fibres. [source]

Recruitment of Ca2+ release channels by calcium-induced Ca2+ release does not appear to occur in isolated Ca2+ release sites in frog skeletal muscle

THE JOURNAL OF PHYSIOLOGY, Issue 3 2002
Karine Fénelon
Ca2+ release from the sarcoplasmic reticulum (SR) in skeletal muscle in response to small depolarisations (e.g. to -60 mV) should be the sum of release from many isolated Ca2+ release sites. Each site has one SR Ca2+ release channel activated by its associated T-tubular voltage sensor. The aim of this study was to evaluate whether it also includes neighbouring Ca2+ release channels activated by Ca-induced Ca2+ release (CICR). Ca2+ release in frog cut muscle fibres was estimated with the EGTA/phenol red method. The fraction of SR Ca content ([CaSR]) released by a 400 ms pulse to -60 mV (denoted fCa) provided a measure of the average Ca2+ permeability of the SR associated with the pulse. In control experiments, fCa was approximately constant when [CaSR] was 1500-3000 ,m (plateau region) and then increased as [CaSR] decreased, reaching a peak when [CaSR] was 300-500 ,m that was 4.8 times larger on average than the plateau value. With 8 mm of the fast Ca2+ buffer BAPTA in the internal solution, fCa was 5.0-5.3 times larger on average than the plateau value obtained before adding BAPTA when [CaSR] was 300-500 ,m. In support of earlier results, 8 mm BAPTA did not affect Ca2+ release in the plateau region. At intermediate values of [CaSR], BAPTA resulted in a small, if any, increase in fCa, presumably by decreasing Ca inactivation of Ca2+ release. Since BAPTA never decreased fCa, the results indicate that neighbouring channels are not activated by CICR with small depolarisations when [CaSR] is 300-3000 ,m. [source]

EXCITATION,CONTRACTION COUPLING FROM THE 1950s INTO THE NEW MILLENNIUM

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2006
AF Dulhunty
SUMMARY 1Excitation,contraction coupling is broadly defined as the process linking the action potential to contraction in striated muscle or, more narrowly, as the process coupling surface membrane depolarization to Ca2+ release from the sarcoplasmic reticulum. 2We now know that excitation,contraction coupling depends on a macromolecular protein complex or ,calcium release unit'. The complex extends the extracellular space within the transverse tubule invaginations of the surface membrane, across the transverse tubule membrane into the cytoplasm and then across the sarcoplasmic reticulum membrane and into the lumen of the sarcoplasmic reticulum. 3The central element of the macromolecular complex is the ryanodine receptor calcium release channel in the sarcoplasmic reticulum membrane. The ryanodine receptor has recruited a surface membrane L-type calcium channel as a ,voltage sensor' to detect the action potential and the calcium-binding protein calsequestrin to detect in the environment within the sarcoplasmic reticulum. Consequently, the calcium release channel is able to respond to surface depolarization in a manner that depends on the Ca2+ load within the calcium store. 4The molecular components of the ,calcium release unit' are the same in skeletal and cardiac muscle. However, the mechanism of excitation,contraction coupling is different. The signal from the voltage sensor to ryanodine receptor is chemical in the heart, depending on an influx of external Ca2+ through the surface calcium channel. In contrast, conformational coupling links the voltage sensor and the ryanodine receptor in skeletal muscle. 5Our current understanding of this amazingly efficient molecular signal transduction machine has evolved over the past 50 years. None of the proteins had been identified in the 1950s; indeed, there was debate about whether the molecules involved were, in fact, protein. Nevertheless, a multitude of questions about the molecular interactions and structures of the proteins and their interaction sites remain to be answered and provide a challenge for the next 50 years. [source]

Excitation,Contraction Coupling In Skeletal Muscle: Comparisons With Cardiac Muscle

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 3 2000
Gd Lamb
SUMMARY 1. The present review describes the mechanisms involved in controlling Ca2+ release from the sarcoplasmic reticulum (SR) of skeletal muscle, which ultimately regulates contraction. 2. Comparisons are made between cardiac and skeletal muscle with respect to: (i) the role of the dihydropyridine receptors (DHPR) as Ca2+ channels and voltage-sensors; (ii) the regulation of the ryanodine receptor (RyR)/Ca2+ -release channels in the SR; and (iii) the importance of Ca2+ -induced Ca2+ release. 3. It is shown that the key differences of the skeletal muscle Ca2+ -release channel (RyR1), namely the increase in its stimulation by ATP and its inhibition by Mg2+, are critical for its direct regulation by the associated DHPR and, consequently, for the fast, accurate control of skeletal muscle contraction. [source]

Caffeine administration results in greater tension development in previously fatigued canine muscle in situ

EXPERIMENTAL PHYSIOLOGY, Issue 6 2005
Richard A. Howlett
In isolated single skeletal myocytes undergoing long-term fatiguing contractions, caffeine (CAF) can result in nearly immediate restoration of generated tension to near-prefatigue levels by increasing Ca2+ release via activation of sarcoplasmic reticulum release channels. This study tested whether arterial CAF infusion (>5 mm) would cause a similar rapid restoration of tetanic isometric tension during contractions to fatigue in perfused canine hindlimb muscle in situ. Tetanic contractions were elicited by electrical stimulation (200 ms trains, 50 Hz, 1 contraction s,1), and biopsies were taken from the muscle at rest and during contractions: (1) following the onset of fatigue (tension ,60% of initial value); and (2) following CAF administration. Resting muscle ATP, PCr and lactate contents were 25.2 ± 0.4, 76.9 ± 3.3 and 14.4 ± 3.3 mmol (kg dry weight),1, respectively. At fatigue, generated tetanic tension was 61.1 ± 6.9% of initial contractions. There was a small but statistically significant recovery of tetanic tension (64.9 ± 6.6% of initial value) with CAF infusion, after which the muscle showed incomplete relaxation. At fatigue, muscle ATP and PCr contents had fallen significantly (P < 0.05) to 18.1 ± 1.1 and 18.9 ± 2.1 mmol (kg dry weight),1, respectively, and lactate content had increased significantly to 27.7 ± 5.4 mmol (kg dry weight),1. Following CAF, skeletal muscle ATP and PCr contents were significantly lower than corresponding fatigue values (15.0 ± 1.3 and 10.9 ± 2.2 mmol (kg dry weight),1, respectively), while lactate was unchanged (22.2 ± 3.9 mmol (kg dry weight),1). These results demonstrate that caffeine can result in a small, but statistically significant, recovery of isometric tension in fatigued canine hindlimb muscle in situ, although not nearly to the same degree as seen in isolated single muscle fibres. This suggests that, in this in situ isolated whole muscle model, alteration of Ca2+ metabolism is probably only one cause of fatigue. [source]

Sarcoplasmic reticulum: The dynamic calcium governor of muscle

MUSCLE AND NERVE, Issue 6 2006
Ann E. Rossi MS
Abstract The sarcoplasmic reticulum (SR) provides feedback control required to balance the processes of calcium storage, release, and reuptake in skeletal muscle. This balance is achieved through the concerted action of three major classes of SR calcium-regulatory proteins: (1) luminal calcium-binding proteins (calsequestrin, histidine-rich calcium-binding protein, junctate, and sarcalumenin) for calcium storage; (2) SR calcium release channels (type 1 ryanodine receptor or RyR1 and IP3 receptors) for calcium release; and (3) sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA) pumps for calcium reuptake. Proper calcium storage, release, and reuptake are essential for normal skeletal muscle function. We review SR structure and function during normal skeletal muscle activity, the proteins that orchestrate calcium storage, release, and reuptake, and how phenotypically distinct muscle diseases (e.g., malignant hyperthermia, central core disease, and Brody disease) can result from subtle alterations in the activity of several key components of the SR calcium-regulatory machinery. Muscle Nerve, 2006 [source]

Comparison of the myoplasmic calcium transient elicited by an action potential in intact fibres of mdx and normal mice

THE JOURNAL OF PHYSIOLOGY, Issue 21 2008
Stephen Hollingworth
The myoplasmic free [Ca2+] transient elicited by an action potential (,[Ca2+]) was compared in fast-twitch fibres of mdx (dystrophin null) and normal mice. Methods were used that maximized the likelihood that any detected differences apply in vivo. Small bundles of fibres were manually dissected from extensor digitorum longus muscles of 7- to 14-week-old mice. One fibre within a bundle was microinjected with furaptra, a low-affinity rapidly responding fluorescent calcium indicator. A fibre was accepted for study if it gave a stable, all-or-nothing fluorescence response to an external shock. In 18 normal fibres, the peak amplitude and the full-duration at half-maximum (FDHM) of ,[Ca2+] were 18.4 ± 0.5 ,m and 4.9 ± 0.2 ms, respectively (mean ±s.e.m.; 16°C). In 13 mdx fibres, the corresponding values were 14.5 ± 0.6 ,m and 4.7 ± 0.2 ms. The difference in amplitude is statistically highly significant (P= 0.0001; two-tailed t test), whereas the difference in FDHM is not (P= 0.3). A multi-compartment computer model was used to estimate the amplitude and time course of the sarcoplasmic reticulum (SR) calcium release flux underlying ,[Ca2+]. Estimates were made based on several differing assumptions: (i) that the resting myoplasmic free Ca2+ concentration ([Ca2+]R) and the total concentration of parvalbumin ([ParvT]) are the same in mdx and normal fibres, (ii) that [Ca2+]R is larger in mdx fibres, (iii) that [ParvT] is smaller in mdx fibres, and (iv) that [Ca2+]R is larger and [ParvT] is smaller in mdx fibres. According to the simulations, the 21% smaller amplitude of ,[Ca2+] in mdx fibres in combination with the unchanged FDHM of ,[Ca2+] is consistent with mdx fibres having a ,25% smaller flux amplitude, a 6,23% larger FDHM of the flux, and a 9,20% smaller total amount of released Ca2+ than normal fibres. The changes in flux are probably due to a change in the gating of the SR Ca2+ -release channels and/or in their single channel flux. The link between these changes and the absence of dystrophin remains to be elucidated. [source]

Local recovery of Ca2+ release in rat ventricular myocytes

THE JOURNAL OF PHYSIOLOGY, Issue 2 2005
Eric A. Sobie
Excitation,contraction coupling in the heart depends on the positive feedback process of Ca2+ -induced Ca2+ release (CICR). While CICR provides for robust triggering of Ca2+ sparks, the mechanisms underlying their termination remain unknown. At present, it is unclear how a cluster of Ca2+ release channels (ryanodine receptors or RyRs) can be made to turn off when their activity is sustained by the Ca2+ release itself. We use a novel experimental approach to investigate indirectly this issue by exploring restitution of Ca2+ sparks. We exploit the fact that ryanodine can bind, nearly irreversibly, to an RyR subunit (monomer) and increase the open probability of the homotetrameric channel. By applying low concentrations of ryanodine to rat ventricular myocytes, we observe repeated activations of individual Ca2+ spark sites. Examination of these repetitive Ca2+ sparks reveals that spark amplitude recovers with a time constant of 91 ms whereas the sigmoidal recovery of triggering probability lags behind amplitude recovery by ,80 ms. We conclude that restitution of Ca2+ sparks depends on local refilling of SR stores after depletion and may also depend on another time-dependent process such as recovery from inactivation or a slow conformational change after rebinding of Ca2+ to SR regulatory proteins. [source]

Disruption of excitation,contraction coupling and titin by endogenous Ca2+ -activated proteases in toad muscle fibres

THE JOURNAL OF PHYSIOLOGY, Issue 3 2005
Esther Verburg
This study investigated the effects of elevated, physiological levels of intracellular free [Ca2+] on depolarization-induced force responses, and on passive and active force production by the contractile apparatus in mechanically skinned fibres of toad iliofibularis muscle. Excitation,contraction (EC) coupling was retained after skinning and force responses could be elicited by depolarization of the transverse-tubular (T-) system. Raising the cytoplasmic [Ca2+] to ,1 ,m or above for 3 min caused an irreversible reduction in the depolarization-induced force response by interrupting the coupling between the voltage sensors in the T-system and the Ca2+ release channels in the sarcoplasmic reticulum. This uncoupling showed a steep [Ca2+] dependency, with 50% uncoupling at ,1.9 ,m Ca2+. The uncoupling occurring with 2 ,m Ca2+ was largely prevented by the calpain inhibitor leupeptin (1 mm). Raising the cytoplasmic [Ca2+] above 1 ,m also caused an irreversible decline in passive force production in stretched skinned fibres in a manner graded by [Ca2+], though at a much slower relative rate than loss of coupling. The progressive loss of passive force could be rapidly stopped by lowering [Ca2+] to 10 nm, and was almost completely inhibited by 1 mm leupeptin but not by 10 ,m calpastatin. Muscle homogenates preactivated by Ca2+ exposure also evidently contained a diffusible factor that caused damage to passive force production in a Ca2+ -dependent manner. Western blotting showed that: (a) calpain-3 was present in the skinned fibres and was activated by the Ca2+exposure, and (b) the Ca2+ exposure in stretched skinned fibres resulted in proteolysis of titin. We conclude that the disruption of EC coupling occurring at elevated levels of [Ca2+] is likely to be caused at least in part by Ca2+ -activated proteases, most likely by calpain-3, though a role of calpain-1 is not excluded. [source]

Recruitment of Ca2+ release channels by calcium-induced Ca2+ release does not appear to occur in isolated Ca2+ release sites in frog skeletal muscle

Dynamics of ionic activities in the apoplast of the sub-stomatal cavity of intact Vicia faba leaves during stomatal closure evoked by ABA and darkness

THE PLANT JOURNAL, Issue 3 2000
Hubert H. Felle
Summary Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl,, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mm (K+), 1.26 mm (Cl,), 64 µm (Ca2+) and 89 µm (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9,10 min, in which Ca2+ and H+ activities transiently decreased, and Cl, and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl, activities completely recovered, while K+ activity approached an elevated level of around 10 mm within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl, and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl, and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mm, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl, and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels. [source]