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1.
To better understand the role of the transient expression of ryanodine receptor (RyR) type 3 (RyR3) on Ca2+ homeostasis during the development of skeletal muscle, we have analyzed the effect of expression levels of RyR3 and RyR1 on the overall physiology of cultured myotubes and muscle fibers. Dyspedic myotubes were infected with RyR1 or RyR3 containing virions at 0.2, 0.4, 1.0, and 4.0 moieties of infection (MOI), and analysis of their pattern of expression, caffeine sensitivity, and resting free Ca2+ concentration ([Ca2+]r) was performed. Although increased MOI resulted in increased expression of each receptor isoform, it did not significantly affect the immunopattern of RyRs or the expression levels of calsequestrin, triadin, or FKBP-12. Interestingly, myotubes expressing RyR3 always had significantly higher [Ca2+]r and lower caffeine EC50 than did cells expressing RyR1. Although some of the increased sensitivity of RyR3 to caffeine could be attributed to the higher [Ca2+]r in RyR3-expressing cells, studies of [3H]ryanodine binding demonstrated intrinsic differences in caffeine sensitivity between RyR1 and RyR3. Tibialis anterior (TA) muscle fibers at different stages of postnatal development exhibited a transient increase in [Ca2+]r coordinately with their level of RyR3 expression. Similarly, adult soleus fibers, which also express RyR3, had higher [Ca2+]r than did adult TA fibers, which exclusively express RyR1. These data show that in skeletal muscle, RyR3 increases [Ca2+]r more than RyR1 does at any expression level. These data suggest that the coexpression of RyR1 and RyR3 at different levels may constitute a novel mechanism by which to regulate [Ca2+]r in skeletal muscle. ryanodine receptor; calcium release; ryanodine binding; muscle fibers 相似文献
2.
Yang T Esteve E Pessah IN Molinski TF Allen PD López JR 《American journal of physiology. Cell physiology》2007,292(5):C1591-C1598
Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle triggered in susceptible individuals by inhalation anesthetics and depolarizing skeletal muscle relaxants. This syndrome has been linked to a missense mutation in the type 1 ryanodine receptor (RyR1) in more than 50% of cases studied to date. Using double-barreled Ca2+ microelectrodes in myotubes expressing wild-type RyR1 (WTRyR1) or RyR1 with one of four common MH mutations (MHRyR1), we measured resting intracellular Ca2+ concentration ([Ca2+]i). Changes in resting [Ca2+]i produced by several drugs known to modulate the RyR1 channel complex were investigated. We found that myotubes expressing any of the MHRyR1s had a 2.0- to 3.7-fold higher resting [Ca2+]i than those expressing WTRyR1. Exposure of myotubes expressing MHRyR1s to ryanodine (500 µM) or (2,6-dichloro-4-aminophenyl)isopropylamine (FLA 365; 20 µM) had no effects on their resting [Ca2+]i. However, when myotubes were exposed to bastadin 5 alone or to a combination of ryanodine and bastadin 5, the resting [Ca2+]i was significantly reduced (P < 0.01). Interestingly, the percent decrease in resting [Ca2+]i in myotubes expressing MHRyR1s was significantly greater than that for WTRyR1. From these data, we propose that the high resting myoplasmic [Ca2+]i in MHRyR1 expressing myotubes is due in part to a related structural conformation of MHRyR1s that favors "passive" calcium leak from the sarcoplasmic reticulum. ryanodine; FLA 365; bastadin 5; resting intracellular calcium concentration; sarcoplasmic reticulum 相似文献
3.
Gallant EM Hart J Eager K Curtis S Dulhunty AF 《American journal of physiology. Cell physiology》2004,286(4):C821-C830
Enhanced sensitivity to caffeine is part of the standard tests for susceptibility to malignant hyperthermia (MH) in humans and pigs. The caffeine sensitivity of skeletal muscle contraction and Ca2+ release from the sarcoplasmic reticulum is enhanced, but surprisingly, the caffeine sensitivity of purified porcine ryanodine receptor Ca2+-release channels (RyRs) is not affected by the MH mutation (Arg615Cys). In contrast, we show here that native malignant hyperthermic pig RyRs (incorporated into lipid bilayers with RyR-associated lipids and proteins) were activated by caffeine at 100- to 1,000-fold lower concentrations than native normal pig RyRs. In addition, the results show that the mutant ryanodine receptor channels were less sensitive to high-affinity activation by a peptide (CS) that corresponds to a part of the IIIII loop of the skeletal dihydropyridine receptor (DHPR). Furthermore, subactivating concentrations of peptide CS enhanced the response of normal pig and rabbit RyRs to caffeine. In contrast, the caffeine sensitivity of MH RyRs was not enhanced by the peptide. These novel results showed that in MH-susceptible pig muscles 1) the caffeine sensitivity of native RyRs was enhanced, 2) the sensitivity of RyRs to a skeletal IIIII loop peptide was depressed, and 3) an interaction between the caffeine and peptide CS activation mechanisms seen in normal RyRs was lost. calcium ion homeostasis; excitation-contraction coupling; ryanodine receptor polymorphisms; muscle contraction 相似文献
4.
Weiss RG O'Connell KM Flucher BE Allen PD Grabner M Dirksen RT 《American journal of physiology. Cell physiology》2004,287(4):C1094-C1102
Malignant hyperthermia (MH) is an inherited pharmacogenetic disorder caused by mutations in the skeletal muscle ryanodine receptor (RyR1) and the dihydropyridine receptor (DHPR) 1S-subunit. We characterized the effects of an MH mutation in the DHPR cytoplasmic III-IV loop of 1S (R1086H) on DHPR-RyR1 coupling after reconstitution in dysgenic (1S null) myotubes. Compared with wild-type 1S, caffeine-activated Ca2+ release occurred at approximately fivefold lower concentrations in nonexpressing and R1086H-expressing myotubes. Although maximal voltage-gated Ca2+ release was similar in 1S- and R1086H-expressing myotubes, the voltage dependence of Ca2+ release was shifted 5 mV to more negative potentials in R1086H-expressing myotubes. Our results demonstrate that 1S functions as a negative allosteric modulator of release channel activation by caffeine/voltage and that the R1086H MH mutation in the intracellular III-IV linker disrupts this negative regulatory influence. Moreover, a low caffeine concentration (2 mM) caused a similar shift in voltage dependence of Ca2+ release in 1S- and R1086H-expressing myotubes. Compared with 1S-expressing myotubes, maximal L channel conductance (Gmax) was reduced in R1086H-expressing myotubes (1S 130 ± 10.2, R1086H 88 ± 6.8 nS/nF; P < 0.05). The decrease in Gmax did not result from a change in retrograde coupling with RyR1 as maximal conductance-charge movement ratio (Gmax/Qmax) was similar in 1S- and R1086H-expressing myotubes and a similar decrease in Gmax was observed for an analogous mutation engineered into the cardiac L channel (R1217H). In addition, both R1086H and R1217H DHPRs targeted normally and colocalized with RyR1 in sarcoplasmic reticulum (SR)-sarcolemmal junctions. These results indicate that the R1086H MH mutation in 1S enhances RyR1 sensitivity to activation by both endogenous (voltage sensor) and exogenous (caffeine) activators. excitation-contraction coupling; calcium channel; muscle disease 相似文献
5.
Bull R Finkelstein JP Humeres A Behrens MI Hidalgo C 《American journal of physiology. Cell physiology》2007,293(1):C162-C171
Despite their relevance for neuronal Ca2+-induced Ca2+ release (CICR), activation by Ca2+ of ryanodine receptor (RyR) channels of brain endoplasmic reticulum at the [ATP], [Mg2+], and redox conditions present in neurons has not been reported. Here, we studied the effects of varying cis-(cytoplasmic) free ATP concentration ([ATP]), [Mg2+], and RyR redox state on the Ca2+ dependence of endoplasmic reticulum RyR channels from rat brain cortex. At pCa 4.9 and 0.5 mM adenylylimidodiphosphate (AMP-PNP), increasing free [Mg2+] up to 1 mM inhibited vesicular [3H]ryanodine binding; incubation with thimerosal or dithiothreitol decreased or enhanced Mg2+ inhibition, respectively. Single RyR channels incorporated into lipid bilayers displayed three different Ca2+ dependencies, defined by low, moderate, or high maximal fractional open time (Po), that depend on RyR redox state, as we have previously reported. In all cases, cis-ATP addition (3 mM) decreased threshold [Ca2+] for activation, increased maximal Po, and shifted channel inhibition to higher [Ca2+]. Conversely, at pCa 4.5 and 3 mM ATP, increasing cis-[Mg2+] up to 1 mM inhibited low activity channels more than moderate activity channels but barely modified high activity channels. Addition of 0.5 mM free [ATP] plus 0.8 mM free [Mg2+] induced a right shift in Ca2+ dependence for all channels so that [Ca2+] <30 µM activated only high activity channels. These results strongly suggest that channel redox state determines RyR activation by Ca2+ at physiological [ATP] and [Mg2+]. If RyR behave similarly in living neurons, cellular redox state should affect RyR-mediated CICR. Ca2+-induced Ca2+ release; Ca2+ release channels; endoplasmic reticulum; thimerosal; 2,4-dithiothreitol; ryanodine receptor 相似文献
6.
Altered Ca(2+) handling by ryanodine receptor and Na(+)-Ca(2+) exchange in the heart from ovariectomized rats: role of protein kinase A 总被引:1,自引:0,他引:1
Kravtsov GM Kam KW Liu J Wu S Wong TM 《American journal of physiology. Cell physiology》2007,292(5):C1625-C1635
Our previous study has demonstrated that ovariectomy (Ovx) significantly increased the left ventricular developed pressure (LVDP) and the maximal rate of developed pressure over time (±dP/dtmax) in the isolated perfused rat heart and the effects were reversed by female sex hormone replacement. In the present investigation, we studied the effects of Ovx for 6 wk on Ca2+ homeostasis that determines the contractile function. Particular emphasis was given to Ca2+ handling by ryanodine receptor (RyR) and Na+-Ca2+ exchange (NCX). 45Ca2+ fluxes via the RyR, NCX, and Ca2+-ATPase (SERCA) were compared with their expression in myocytes from Ovx rats with and without estrogen replacement. Furthermore, we correlated the handling of Ca2+ by these Ca2+ handling proteins with the overall Ca2+ homeostasis by determining the Ca2+ transients induced by electrical stimulation and caffeine, which reveals the dynamic changes of cytosolic Ca2+ concentration ([Ca2+]i) in the heart. In addition, we determined the expression and contribution of protein kinase A (PKA) to the regulation of the aforementioned Ca2+ handling proteins in Ovx rats. It was found that after Ovx there were 1) increased Ca2+ fluxes via RyR and NCX, which were reversed not only by estrogen replacement, but more importantly by blockade of PKA; 2) an increased expression of PKA; and 3) no increase in expression of NCX and SERCA. We suggest that hyperactivities of RyR and NCX are a result of upregulation of PKA. The increased release of Ca2+ through RyR and removal of Ca2+ by NCX are believed to be responsible for the greater contractility and faster relaxation after Ovx. ovariectomy 相似文献
7.
Activation of calcium release assessed by calcium release-induced inactivation of calcium current in rat cardiac myocytes 总被引:4,自引:0,他引:4
Zahradníková A Kubalová Z Pavelková J Györke S Zahradník I 《American journal of physiology. Cell physiology》2004,286(2):C330-C341
In mammalian cardiac myocytes, calcium released into the dyadic space rapidly inactivates calcium current (ICa). We used this Ca2+ release-dependent inactivation (RDI) of ICa as a local probe of sarcoplasmic reticulum Ca2+ release activation. In whole cell patch-clamped rat ventricular myocytes, Ca2+ entry induced by short prepulses from 50 mV to positive voltages caused suppression of peak ICa during a test pulse. The negative correlation between peak ICa suppression and ICa inactivation during the test pulse indicated that RDI evoked by the prepulse affected only calcium channels in those dyads in which calcium release was activated. Ca2+ ions injected during the prepulse and during the subsequent tail current suppressed peak ICa in the test pulse to a different extent. Quantitative analysis indicated that equal Ca2+ charge was 3.5 times less effective in inducing release when entering during the prepulse than when entering during the tail. Tail Ca2+ charge injected by the first voltage-dependent calcium channel (DHPR) openings was three times less effective than that injected by DHPR reopenings. These findings suggest that calcium release activation can be profoundly influenced by the recent history of L-type Ca2+ channel activity due to potentiation of ryanodine receptors (RyRs) by previous calcium influx. This conclusion was confirmed at the level of single RyRs in planar lipid bilayers: using flash photolysis of the calcium cage NP-EGTA to generate two sequential calcium stimuli, we showed that RyR activation in response to the second stimulus was four times higher than that in response to the first stimulus. excitation-contraction coupling 相似文献
8.
RyR1 exhibits lower gain of CICR activity than RyR3 in the SR: evidence for selective stabilization of RyR1 channel 总被引:1,自引:0,他引:1
We showed that frog -ryanodine receptor (-RyR) had a lower gain of Ca2+-induced Ca2+ release (CICR) activity than -RyR in sarcoplasmic reticulum (SR) vesicles, indicating selective "stabilization" of the former isoform (Murayama T and Ogawa Y. J Biol Chem 276: 29532960, 2001). To know whether this is also the case with mammalian RyR1, we determined [3H]ryanodine binding of RyR1 and RyR3 in bovine diaphragm SR vesicles. The value of [3H]ryanodine binding (B) was normalized by the number of maximal binding sites (Bmax), whereby the specific activity of each isoform was expressed. This B/Bmax expression demonstrated that ryanodine binding of individual channels for RyR1 was <15% that for RyR3. Responses to Ca2+, Mg2+, adenine nucleotides, and caffeine were not substantially different between in situ and purified isoforms. These results suggest that the gain of CICR activity of RyR1 is markedly lower than that of RyR3 in mammalian skeletal muscle, indicating selective stabilization of RyR1 as is true of frog -RyR. The stabilization was partly eliminated by FK506 and partly by solubilization of the vesicles with CHAPS, each of which was additive to the other. In contrast, high salt, which greatly enhances [3H]ryanodine binding, caused only a minor effect on the stabilization of RyR1. None of the T-tubule components, coexisting RyR3, or calmodulin was the cause. The CHAPS-sensitive intra- and intermolecular interactions that are common between mammalian and frog skeletal muscles and the isoform-specific inhibition by FKBP12, which is characteristic of mammals, are likely to be the underlying mechanisms. excitation-contraction coupling; ryanodine binding; ryanodine receptor 相似文献
9.
Mauban JR Wilkinson K Schach C Yuan JX 《American journal of physiology. Cell physiology》2006,290(2):C325-C336
Agonist stimulation of human pulmonary artery smooth muscle cells (PASMC) and endothelial cells (PAEC) with histamine showed similar spatiotemporal patterns of Ca2+ release. Both sustained elevation and oscillatory patterns of changes in cytosolic Ca2+ concentration ([Ca2+]cyt) were observed in the absence of extracellular Ca2+. Capacitative Ca2+ entry (CCE) was induced in PASMC and PAEC by passive depletion of intracellular Ca2+ stores with 10 µM cyclopiazonic acid (CPA; 1530 min). The pyrazole derivative BTP2 inhibited CPA-activated Ca2+ influx, suggesting that depletion of CPA-sensitive internal stores is sufficient to induce CCE in both PASMC and PAEC. The recourse of histamine-mediated Ca2+ release was examined after exposure of cells to CPA, thapsigargin, caffeine, ryanodine, FCCP, or bafilomycin. In PASMC bathed in Ca2+-free solution, treatment with CPA almost abolished histamine-induced rises in [Ca2+]cyt. In PAEC bathed in Ca2+-free solution, however, treatment with CPA eliminated histamine-induced sustained and oscillatory rises in [Ca2+]cyt but did not affect initial transient increase in [Ca2+]cyt. Furthermore, treatment of PAEC with a combination of CPA (or thapsigargin) and caffeine (and ryanodine), FCCP, or bafilomycin did not abolish histamine-induced transient [Ca2+]cyt increases. These observations indicate that 1) depletion of CPA-sensitive stores is sufficient to cause CCE in both PASMC and PAEC; 2) induction of CCE in PAEC does not require depletion of all internal Ca2+ stores; 3) the histamine-releasable internal stores in PASMC are mainly CPA-sensitive stores; 4) PAEC, in addition to a CPA-sensitive functional pool, contain other stores insensitive to CPA, thapsigargin, caffeine, ryanodine, FCCP, and bafilomycin; and 5) although the CPA-insensitive stores in PAEC may not contribute to CCE, they contribute to histamine-mediated Ca2+ release. intracellular calcium stores; oscillations; pulmonary hypertension 相似文献
10.
All three ryanodine receptor isoforms generate rapid cooling responses in muscle cells 总被引:1,自引:0,他引:1
Protasi F Shtifman A Julian FJ Allen PD 《American journal of physiology. Cell physiology》2004,286(3):C662-C670
The rapid cooling (RC) response in muscle is an increase in cytoplasmic Ca2+ concentration ([Ca2+]i) that is probably caused by Ca2+ release from the sarcoplasmic reticulum (SR). However, the molecular bases of this response have not been completely elucidated. Three different isoforms of the SR Ca2+ release channels, or ryanodine receptors (RyRs), have been isolated (RyR1, RyR2, and RyR3). In the current investigation, the RC response was studied in RyR-null muscle cells (1B5) before and after transduction with HSV-1 virions containing the cDNAs encoding for RyR1, RyR2, or RyR3. Cells were loaded with fluo 4-AM to monitor changes in [Ca2+]i and perfused with either cold (0°C), room temperature (RT), or RT buffer containing 40 mM caffeine. Control cells showed no significant response to cold or caffeine, whereas robust Ca2+ transients were recorded in response to both RC and caffeine in transduced cells expressing any one of the three RyR isoforms. Our data demonstrate directly that RyRs are responsible for the RC response and that all three isoforms respond in a similar manner. Ca2+ release from RyRs is likely caused by a RC-induced conformational change of the channel from the closed to the open state. calcium release channel; sarcoplasmic reticulum; excitation-contraction coupling 相似文献
11.
Chugun A Sato O Takeshima H Ogawa Y 《American journal of physiology. Cell physiology》2007,292(1):C535-C544
To clarify whether activity of the ryanodine receptor type 2 (RyR2) is reduced in the sarcoplasmic reticulum (SR) of cardiac muscle, as is the case with the ryanodine receptor type 1 (RyR1), Ca2+-dependent [3H]ryanodine binding, a biochemical measure of Ca2+-induced Ca2+ release (CICR), was determined using SR vesicle fractions isolated from rabbit and rat cardiac muscles. In the absence of an adenine nucleotide or caffeine, the rat SR showed a complicated Ca2+ dependence, instead of the well-documented biphasic dependence of the rabbit SR. In the rat SR, [3H]ryanodine binding initially increased as [Ca2+] increased, with a plateau in the range of 10100 µM Ca2+, and thereafter further increased to an apparent peak around 1 mM Ca2+, followed by a decrease. In the presence of these modulators, this complicated dependence prevailed, irrespective of the source. Addition of 0.31 mM Mg2+ unexpectedly increased the binding two- to threefold and enhanced the affinity for [3H]ryanodine at 10100 µM Ca2+, resulting in the well-known biphasic dependence. In other words, the partial suppression of RyR2 is relieved by Mg2+. Ca2+ could be a substitute for Mg2+. Mg2+ also amplifies the responses of RyR2 to inhibitory and stimulatory modulators. This stimulating effect of Mg2+ on RyR2 is entirely new, and is referred to as the third effect, in addition to the well-known dual inhibitory effects. This effect is critical to describe the role of RyR2 in excitation-contraction coupling of cardiac muscle, in view of the intracellular Mg2+ concentration. [3H]ryanodine binding; CICR; stimulation by physiological Mg2+, excitation-contraction coupling in the heart 相似文献
12.
Bull R Marengo JJ Finkelstein JP Behrens MI Alvarez O 《American journal of physiology. Cell physiology》2003,285(1):C119-C128
We have reported that ryanodine receptor (RyR) channels display three different responses to cytoplasmic free Ca2+ concentration ([Ca2+]) depending on their redox state (Marengo JJ, Hidalgo C, and Bull R. Biophys J 74: 12631277, 1998), with low, moderate, and high maximal fractional open times (Po). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 µM cytoplasmic [Ca2+]. At 10 µM [Ca2+], low-Po channels presented lower apparent affinity to activation by ATP [[ATP] for half-maximal activation (KaATP) = 422 µM] than moderate-Po channels (KaATP = 82 µM). Oxidation of low-Po channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-Po channels and decreased KaATP from 422 to 82 µM. At 0.1 µM cytoplasmic [Ca2+], ATP induced an almost negligible activation of low-Po channels. After oxidation to high-Po behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-Po channels at 10 µM [Ca2+] plus ATP revealed the presence of subconductance states, suggesting a conduction mechanism that involves four independent subchannels. On oxidation the subchannels opened and closed in a concerted mode. subconductance states; calcium ion release channels; calcium ion regulation; thimerosal; 2,2'-dithiodipyridine 相似文献
13.
Role of cyclic ADP-ribose in the regulation of [Ca2+]i in porcine tracheal smooth muscle 总被引:1,自引:0,他引:1
Prakash Y. S.; Kannan Mathur S.; Walseth Timothy F.; Sieck Gary C. 《American journal of physiology. Cell physiology》1998,274(6):C1653
The purpose ofthe present study was to determine whether cyclic ADP-ribose (cADPR)acts as a second messenger forCa2+ release through ryanodinereceptor (RyR) channels in tracheal smooth muscle (TSM). Freshlydissociated porcine TSM cells were permeabilized with -escin, andreal-time confocal microscopy was used to examine changes inintracellular Ca2+ concentration([Ca2+]i).cADPR (10 nM-10 µM) induced a dose-dependent increase in [Ca2+]i,which was blocked by the cADPR receptor antagonist 8-amino-cADPR (20 µM) and by the RyR blockers ruthenium red (10 µM) and ryanodine (10 µM), but not by the inositol 1,4,5-trisphosphate receptor blockerheparin (0.5 mg/ml). During steady-state[Ca2+]ioscillations induced by acetylcholine (ACh), addition of 100 nM and 1 µM cADPR increased oscillation frequency and decreased peak-to-troughamplitude. ACh-induced[Ca2+]ioscillations were blocked by 8-amino-cADPR; however, 8-amino-cADPR didnot block the[Ca2+]iresponse to a subsequent exposure to caffeine. These results indicatethat cADPR acts as a second messenger forCa2+ release through RyR channelsin TSM cells and may be necessary for initiating ACh-induced[Ca2+]ioscillations. 相似文献
14.
Copello JA Zima AV Diaz-Sylvester PL Fill M Blatter LA 《American journal of physiology. Cell physiology》2007,292(6):C2129-C2140
During the cardiac action potential, Ca2+ entry through dyhidropyridine receptor L-type Ca2+ channels (DHPRs) activates ryanodine receptors (RyRs) Ca2+-release channels, resulting in massive Ca2+ mobilization from the sarcoplasmic reticulum (SR). This global Ca2+ release arises from spatiotemporal summation of many localized elementary Ca2+-release events, Ca2+ sparks. We tested whether DHPRs modulate Ca2+sparks in a Ca2+ entry-independent manner. Negative modulation by DHPR of RyRs via physical interactions is accepted in resting skeletal muscle but remains controversial in the heart. Ca2+ sparks were studied in cat cardiac myocytes permeabilized with saponin or internally perfused via a patch pipette. Bathing and pipette solutions contained low Ca2+ (100 nM). Under these conditions, Ca2+ sparks were detected with a stable frequency of 3–5 sparks·s–1·100 µm–1. The DHPR blockers nifedipine, nimodipine, FS-2, and calciseptine decreased spark frequency, whereas the DHPR agonists Bay-K8644 and FPL-64176 increased it. None of these agents altered the spatiotemporal characteristics of Ca2+ sparks. The DHPR modulators were also without effect on SR Ca2+ load (caffeine-induced Ca2+ transients) or sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity (Ca2+ loading rates of isolated SR microsomes) and did not change cardiac RyR channel gating (planar lipid bilayer experiments). In summary, DHPR modulators affected spark frequency in the absence of DHPR-mediated Ca2+ entry. This action could not be attributed to a direct action of DHPR modulators on SERCA or RyRs. Our results suggest that the activity of RyR Ca2+-release units in ventricular myocytes is modulated by Ca2+ entry-independent conformational changes in neighboring DHPRs. exitation-contraction coupling; ryanodine receptor; sarco(endo)plasmic reticulum Ca2+-ATPase; dihydropyridine receptor; sarcoplasmic reticulum 相似文献
15.
López JR Linares N Pessah IN Allen PD 《American journal of physiology. Cell physiology》2005,288(3):C606-C612
Malignant hyperthermia (MH) is a potentially fatal pharmacogenetic syndrome caused by exposure to halogenated volatile anesthetics and/or depolarizing muscle relaxants. We have measured intracellular Ca2+ concentration ([Ca2+]i) using double-barreled, Ca2+-selective microelectrodes in myoballs prepared from skeletal muscle of MH-susceptible (MHS) and MH-nonsusceptible (MHN) swine. Resting [Ca2+]i was approximately twofold in MHS compared with MHN quiescent myoballs (232 ± 35 vs. 112 ± 11 nM). Treatment of myoballs with caffeine or 4-chloro-m-cresol (4-CmC) produced an elevation in [Ca2+]i in both groups; however, the concentration required to cause a rise in [Ca2+]i elevation was four times lower in MHS than in MHN skeletal muscle cells. Incubation of MHS cells with the fast-complexing Ca2+ buffer BAPTA reduced [Ca2+]i, raised the concentration of caffeine and 4-CmC required to cause an elevation of [Ca2+]i, and reduced the amount of Ca2+ release associated with exposure to any given concentration of caffeine or 4-CmC to MHN levels. These results suggest that the differences in the response of MHS skeletal myoballs to caffeine and 4-CmC may be mediated at least in part by the chronic high resting [Ca2+]i levels in these cells. calcium homeostasis; 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid 相似文献
16.
Shtifman Alexander; Paolini Cecilia; Lopez Jose R.; Allen Paul D.; Protasi Feliciano 《American journal of physiology. Cell physiology》2004,286(1):C73
Differentiated primary myotubes isolated from wild-type mice exhibit ryanodine-sensitive, spontaneous global Ca2+ oscillations as well as spontaneous depolarizations in the plasma membrane. Immunolabeling of these myotubes showed expression of both 1S dihydropyridine receptors (DHPRs) and ryanodine-sensitive Ca2+-release channel 1 (RyR1), the two key proteins in skeletal excitation-contraction (E-C) coupling. Spontaneous global Ca2+ oscillations could be inhibited by addition of 0.1 mM CdCl2/0.5 mM LaCl3 or 5 µM nifedipine to the extracellular bathing solution. After either treatment, Ca2+ oscillations could be restored upon extensive washing. Although exposure to DHPR antagonists completely blocked Ca2+ oscillations, normal orthograde signaling between DHPRs and RyRs, such as that elicited by 80 mM KCl depolarization, was still observed. In addition, we showed that spontaneous Ca2+ oscillations were never present in cultured mdg myotubes, which lack the expression of 1SDHPRs. These results suggest that under physiological conditions in conjunction with the mechanical coupling between the 1SDHPRs and RyR1, the initiation of Ca2+ oscillations in myotubes may be facilitated, in part, by the Ca2+ influx through the 1s-subunit of the DHPR. calcium-induced calcium release; dihydropyridine receptors; excitation-contraction coupling; ryanodine receptors; skeletal muscle 相似文献
17.
Yeung HM Kravtsov GM Ng KM Wong TM Fung ML 《American journal of physiology. Cell physiology》2007,292(6):C2046-C2056
This study examined Ca2+ handling mechanisms involved in cardioprotection induced by chronic intermittent hypoxia (CIH) against ischemia-reperfusion (I/R) injury. Adult male Sprague-Dawley rats were exposed to 10% inspired O2 continuously for 6 h daily from 3, 7, and 14 days. In isolated perfused hearts subjected to I/R, CIH-induced cardioprotection was most significant in the 7-day group with less infarct size and lactate dehydrogenase release, compared with the normoxic group. The I/R-induced alterations in diastolic Ca2+ level, amplitude, time-to-peak, and the decay time of both electrically and caffeine-induced Ca2+ transients measured by spectrofluorometry in isolated ventricular myocytes of the 7-day CIH group were less than that of the normoxic group, suggesting an involvement of altered Ca2+ handling of the sarcoplasmic reticulum (SR) and sarcolemma. We further determined the protein expression and activity of 45Ca2+ flux of SR-Ca2+-ATPase, ryanodine receptor (RyR) and sarcolemmal Na+/Ca2+ exchange (NCX) in ventricular myocytes from the CIH and normoxic groups before and during I/R. There were no changes in expression levels of the Ca2+-handling proteins but significant increases in the RyR and NCX activities were remarkable during I/R in the CIH but not the normoxic group. The augmented RyR and NCX activities were abolished, respectively, by PKA inhibitor (0.5 µM KT5720 or 0.5 µM PKI14-22) and PKC inhibitor (5 µM chelerythrine chloride or 0.2 µM calphostin C) but not by Ca2+/calmodulin-dependent protein kinase II inhibitor KN-93 (1 µM). Thus, CIH confers cardioprotection against I/R injury in rat cardiomyocytes by altered Ca2+ handling with augmented RyR and NCX activities via protein kinase activation. cardioprotection; intracellular calcium 相似文献
18.
Lamb GD El-Hayek R Ikemoto N Stephenson DG 《American journal of physiology. Cell physiology》2000,279(4):C891-C905
Inskeletal muscle fibers, the intracellular loop between domains II andIII of the 1-subunit of the dihydropyridine receptor (DHPR) may directly activate the adjacent Ca2+ releasechannel in the sarcoplasmic reticulum. We examined the effects ofsynthetic peptide segments of this loop on Ca2+ release inmechanically skinned skeletal muscle fibers with functional excitation-contraction coupling. In rat fibers at physiological Mg2+ concentration ([Mg2+]; 1 mM), a20-residue skeletal muscle DHPR peptide[AS(20);Thr671-Leu690; 30 µM], shown previously toinduce Ca2+ release in a triad preparation, caused onlysmall spontaneous force responses in ~40% of fibers, although itpotentiated responses to depolarization and caffeine in all fibers. TheCOOH-terminal half of AS(20)[AS(10)] induced much larger spontaneousresponses but also caused substantial inhibition of Ca2+release to both depolarization and caffeine. Both peptides induced orpotentiated Ca2+ release even when the voltage sensors wereinactivated, indicating direct action on the Ca2+ releasechannels. The corresponding 20-residue cardiac DHPR peptide [AC(20);Thr793-Ala812] was ineffective, but itsCOOH-terminal half [AC(10)] had effects similar to AS(20). In the presence of lower[Mg2+] (0.2 mM), exposure to eitherAS(20) or AC(10) (30 µM) induced substantial Ca2+ release. PeptideCS (100 µM), a loop segment reported to inhibit Ca2+ release in triads, caused partial inhibition ofdepolarization-induced Ca2+ release. In toad fibers, eachof the A peptides had effects similar to or greater than those in ratfibers. These findings suggest that the A and C regions of the skeletalDHPR II-III loop may have important roles in vivo. 相似文献
19.
Balog Edward M.; Gallant Esther M. 《American journal of physiology. Cell physiology》1999,276(1):C128
Modulation of the L-type current by sarcoplasmicreticulum (SR) Ca2+ release hasbeen examined in patch-clamped mouse myotubes. Inhibition of SRCa2+ release by inclusion ofryanodine in the internal solution shifted the half-activating voltage(V0.5) of theL-type current from 1.1 ± 2.1 to 7.7 ± 1.7 mV. Rutheniumred in the internal solution shiftedV0.5 from 5.4 ± 1.9 to 3.2 ± 4.1 mV. Chelation of myoplasmic Ca2+ with1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraaceticacid perfusion shiftedV0.5 from 4.4 ± 1.7 to 3.5 ± 3.3 mV and increased the peak current.Extracellular caffeine (1 mM), which should enhance SRCa2+ release, significantlydecreased the peak Ca2+ current.In low (0.1 mM) internal EGTA, myotube contraction was abolished byinternal perfusion with ryanodine or ruthenium red, whereas addition ofcaffeine to the extracellular solution lowered the contractilethreshold, indicating that these modulators of SRCa2+ release had the expectedeffects on contraction. Therefore, SR Ca2+ release appears to modulatethe sarcolemmal L-type current, suggesting a retrograde communicationfrom the SR to the sarcolemmal L-type channels inexcitation-contraction coupling. 相似文献
20.
Changes in intracellular Ca2+ concentration induced by L-type Ca2+ channel current in guinea pig gastric myocytes 总被引:1,自引:0,他引:1
Kim Sung Joon; Ahn Seung Cheol; Kim Jin Kyung; Kim Young Chul; So Insuk; Kim Ki Whan 《American journal of physiology. Cell physiology》1997,273(6):C1947
We investigatedthe relationship between voltage-operatedCa2+ channel current and thecorresponding intracellular Ca2+concentration([Ca2+]i)change (Ca2+ transient) in guineapig gastric myocytes. Fluorescence microspectroscopy was combined withconventional whole cell patch-clamp technique, and fura 2 (80 µM) wasadded to CsCl-rich pipette solution. Step depolarization to 0 mVinduced inward Ca2+ current(ICa) andconcomitantly raised[Ca2+]i.Both responses were suppressed by nicardipine, an L-typeCa2+ channel blocker, and thevoltage dependence of Ca2+transient was similar to the current-voltage relation ofICa. When pulseduration was increased by up to 900 ms, peakCa2+ transient increased andreached a steady state when stimulation was for longer. The calculatedfast Ca2+ buffering capacity(B value), determined as the ratio ofthe time integral ofICa divided bythe amplitude of Ca2+ transient,was not significantly increased after depletion of Ca2+ stores by the cyclicapplication of caffeine (10 mM) in the presence of ryanodine (4 µM).The addition of cyclopiazonic acid (CPA, 10 µM), a sarco(endo)plasmicreticulum Ca2+-ATPase inhibitor,decreased B value by ~20% in areversible manner. When KCl pipette solution was used,Ca2+-activatedK+ current[IK(Ca)]was also recorded during step depolarization. CPA sensitivelysuppressed the initial peak and oscillations of IK(Ca) withirregular effects on Ca2+transients. The above results suggest that, in guinea pig gastric myocyte, Ca2+ transient is tightlycoupled to ICaduring depolarization, and global[Ca2+]iis not significantly affected byCa2+-inducedCa2+ release from sarcoplasmicreticulum during depolarization. 相似文献