TY - JOUR AU - Collet, C AU - Pouvreau, S AU - Csernoch, László AU - Allard, B AU - Jacquemond, V TI - Calcium signaling in isolated skeletal muscle fibers investigated under "Silicone Voltage-Clamp" conditions JF - CELL BIOCHEMISTRY AND BIOPHYSICS J2 - CELL BIOCHEM BIOPHYS VL - 40 PY - 2004 IS - 2 SP - 225 EP - 236 PG - 12 SN - 1085-9195 DO - 10.1385/CBB:40:2:225 UR - https://m2.mtmt.hu/api/publication/1356318 ID - 1356318 N1 - OD: 2004/04/01 Calcium signaling in isolated skeletal muscle fibers investigated under "Silicone Voltage-Clamp" conditions AN: 15054224 PM: PMCID Collet, Claude; Pouvreau, Sandrine; Csernoch, Laszlo; Allard, Bruno; Jacquemond, Vincent Research Support, Non-U.S. Gov't Review United States Cell biochemistry and biophysics Cell Biochem Biophys. 2004;40(2):225-36. DOI: 10.1385/CBB:40:2:225 eng : Calcium/*metabolism : Calcium Signaling/*physiology : Cell Membrane/*physiology : Cells, Cultured : Humans : Membrane Potentials/*physiology : Muscle Fibers, Skeletal/*metabolism : Muscle, Skeletal/*physiology : Patch-Clamp Techniques/*methods : Silicones ID: 31 Megjegyzés-21018918 Calcium signaling in isolated skeletal muscle fibers investigated under "silicone voltage-clamp" conditions AN: ISI:000220855900009 PM: PMCID ID: 395 Megjegyzés-21019093 ID: 551 Megjegyzés-21019130 Calcium signaling in isolated skeletal muscle fibers investigated under "silicone voltage-clamp" conditions AN: ISI:000220855900009 PM: PMCID ID: 577 Megjegyzés-21019371, ID: 640 Megjegyzés-21129966, ID: 12 ID: 346 AB - In skeletal muscle, release of calcium from the sarcoplasmic reticulum (SR) represents the major source of cytoplasmic Ca2+ elevation. SR calcium release is under the strict command of the membrane potential, which drives the interaction between the voltage sensors in the t-tubule membrane and the calcium-release channels. Either detection or control of the membrane voltage is thus essential when studying intracellular calcium signaling in an intact muscle fiber preparation. The silicone-clamp technique used in combination with intracellular calcium measurements represents an efficient tool for such studies. This article reviews some properties of the plasma membrane and intracellular signals measured with this methodology in mouse skeletal muscle fibers. Focus is given to the potency of this approach to investigate both fundamental aspects of excitation-contraction coupling and potential alterations of intracellular calcium handling in some muscle diseases. LA - English DB - MTMT ER - TY - JOUR AU - Csernoch, László AU - Zhou, J AU - Stern, M D AU - Brum, G AU - Ríos, E TI - The elementary events of Ca2+ release elicited by membrane depolarization in mammalian muscle JF - JOURNAL OF PHYSIOLOGY-LONDON J2 - J PHYSIOL-LONDON VL - 557 PY - 2004 IS - 1 SP - 43 EP - 58 PG - 16 SN - 0022-3751 DO - 10.1113/jphysiol.2003.059154 UR - https://m2.mtmt.hu/api/publication/1356317 ID - 1356317 N1 - Megjegyzés-21019497 May The elementary events of Ca2+ release elicited by membrane depolarization in mammalian muscle AN: ISI:000221649000005 PM: PMCID ID: 731 AB - Cytosolic [Ca(2+)] transients elicited by voltage clamp depolarization were examined by confocal line scanning of rat skeletal muscle fibres. Ca(2+) sparks were observed in the fibres' membrane-permeabilized ends, but not in responses to voltage in the membrane-intact area. Elementary events of the depolarization-evoked response could be separated either at low voltages (near -50 mV) or at -20 mV in partially inactivated cells. These were of lower amplitude, narrower and of much longer duration than sparks, similar to 'lone embers' observed in the permeabilized segments. Their average amplitude was 0.19 and spatial half-width 1.3 microm. Other parameters depended on voltage. At -50 mV average duration was 111 ms and latency 185 ms. At -20 mV duration was 203 ms and latency 24 ms. Ca(2+) release current, calculated on an average of events, was nearly steady at 0.5-0.6 pA. Accordingly, simulations of the fluorescence event elicited by a subresolution source of 0.5 pA open for 100 ms had morphology similar to the experimental average. Because 0.5 pA is approximately the current measured for single RyR channels in physiological conditions, the elementary fluorescence events in rat muscle probably reflect opening of a single RyR channel. A reconstruction of cell-averaged release flux at -20 mV based on the observed distribution of latencies and calculated elementary release had qualitatively correct but slower kinetics than the release flux in prior whole-cell measurements. The qualitative agreement indicates that global Ca(2+) release flux results from summation of these discrete events. The quantitative discrepancies suggest that the partial inactivation strategy may lead to events of greater duration than those occurring physiologically in fully polarized cells. LA - English DB - MTMT ER - TY - JOUR AU - Szentesi, Péter AU - Cserné Szappanos, Henrietta AU - Szegedi, Csaba AU - Gönczi, Mónika AU - Jóna, István AU - Cseri, Julianna AU - Kovács, László AU - Csernoch, László TI - Altered Elementary Calcium Release Events and Enhanced Calcium Release by Thymol in Rat Skeletal Muscle JF - BIOPHYSICAL JOURNAL J2 - BIOPHYS J VL - 86 PY - 2004 IS - 3 SP - 1436 EP - 1453 PG - 18 SN - 0006-3495 DO - 10.1016/S0006-3495(04)74213-7 UR - https://m2.mtmt.hu/api/publication/237015 ID - 237015 N1 - Mar Altered elementary calcium release events and enhanced calcium release by thymol in rat skeletal muscle AN: ISI:000189377400014 PM: PMCID AB - The effects of thymol on steps of excitation-contraction coupling were studied on fast-twitch muscles of rodents. Thymol was found to increase the depolarization-induced release of calcium from the sarcoplasmic reticulum, which could not be attributed to a decreased calcium-dependent inactivation of calcium release channels/ryanodine receptors or altered intramembrane charge movement, but rather to a more efficient coupling of depolarization to channel opening. Thymol increased ryanodine binding to heavy sarcoplasmic reticulum vesicles, with a half-activating concentration of 144M and a Hill coefficient of 1.89, and the open probability of the isolated and reconstituted ryanodine receptors, from 0.090.03 to 0.220.04 at 30M. At higher concentrations the drug induced long-lasting open events on a full conducting state. Elementary calcium release events imaged using laser scanning confocal microscopy in the line-scan mode were reduced in size, 0.920.01 vs. 0.700.01, but increased in duration, 561 vs. 791ms, by 30M thymol, with an increase in the relative proportion of lone embers. Higher concentrations favored long events, resembling embers in control, with duration often exceeding 500ms. These findings provide direct experimental evidence that the opening of a single release channel will generate an ember, rather than a spark, in mammalian skeletal muscle. LA - English DB - MTMT ER - TY - JOUR AU - Collet, C AU - Csernoch, László AU - Jacquemond, V TI - Intramembrane charge movement and L-type calcium current in skeletal muscle fibers isolated from control and mdx mice JF - BIOPHYSICAL JOURNAL J2 - BIOPHYS J VL - 84 PY - 2003 IS - 1 SP - 251 EP - 265 PG - 15 SN - 0006-3495 DO - 10.1016/S0006-3495(03)74846-2 UR - https://m2.mtmt.hu/api/publication/1356322 ID - 1356322 N1 - Megjegyzés-21019097 Jan Intramembrane charge movement and L-type calcium current in skeletal muscle fibers isolated from control and mdx mice AN: ISI:000183067300020 PM: PMCID ID: 558 ID: 348 AB - Dystrophin-deficient muscle fibers from mdx mice are believed to suffer from increased calcium entry and elevated submembranous calcium level, the actual source and functional consequences of which remain obscure. Here we compare the properties of the dihydropyridine receptor as voltage sensor and calcium channel in control and mdx muscle fibers, using the silicone-voltage clamp technique. In control fibers charge movement followed a two-state Boltzmann distribution with values for maximal charge, midpoint voltage, and steepness of 23 +/- 2 nC/ micro F, -37 +/- 3 mV, and 13 +/- 1 mV (n = 7). Essentially identical values were obtained in mdx fibers and the time course of charge recovery from inactivation was also similar in the two populations (tau approximately 6 s). In control fibers the voltage dependence of the slow calcium current elicited by 100-ms-long pulses gave values for maximal conductance, apparent reversal potential, half-activation potential, and steepness factor of 156 +/- 15 S/F, 65.5 +/- 2.9 mV, -0.76 +/- 1.2 mV, and 6.2 +/- 0.5 mV (n = 17). In mdx fibers, the half-activation potential of the calcium current was slightly more negative (-6.2 +/- 1.2 mV, n = 16). Also, when using longer pulses, the time constant of calcium current decay was found to be significantly larger (by a factor of 1.5-2) in mdx than in control fibers. These changes in calcium current properties are unlikely to be primarily responsible for a dramatic alteration of intracellular calcium homeostasis. They may be speculated to result, at least in part, from remodeling of the submembranous cytoskeleton network due to the absence of dystrophin. LA - English DB - MTMT ER - TY - JOUR AU - Collet, Claude AU - Strube, Caroline AU - Csernoch, László AU - Mallouk, Nora AU - Ojeda, Carlos AU - Allard, Bruno AU - Jacquemond, Vincent TI - Effects of extracellular ATP on freshly isolated mouse skeletal muscle cells during pre-natal and post-natal development JF - PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY J2 - PFLUG ARCH EUR J PHY VL - 443 PY - 2002 IS - 5-6 SP - 771 EP - 778 PG - 8 SN - 0031-6768 DO - 10.1007/s00424-001-0758-9 UR - https://m2.mtmt.hu/api/publication/1356326 ID - 1356326 AB - Extracellular adenosine 5'-triphosphate (ATP) has profound effects on membrane conductance and on the intracellular free [Ca(2+)] ([Ca(2+)](i)) in cultured skeletal muscle cells. The aim of the present study was to examine the occurrence and to characterize the properties of such responses during mammalian muscle development in vivo. The effect of ATP (0.2 mM) was tested on membrane current and [Ca(2+)](i) in freshly isolated pre- and post-natal mouse skeletal muscle cells. Pre-natal cells were from 14- to 19-day-old fetuses. In pre- and early post-natal cells, very small elevations of [Ca(2+)](i) (<50 nM) following ATP application could be detected with the fluorescent indicator fura-2. A clear subsarcolemmal rise in [Ca(2+)] was however associated to the presence of ATP, as demonstrated by increased activity of plasma membrane Ca(2+)-activated K(+) channels in cells bathed in a depolarizing, high-calcium-containing solution. In cells voltage-clamped at -80 mV in external Tyrode, ATP induced an inward current associated with an increased membrane conductance. The mean maximal amplitude of the ATP-induced current was -0.84 +/- 0.07 A/F ( n=39). The response to ATP was still present after birth, although its amplitude tended to decrease with post-natal development and was completely absent in muscle cells from 3- to 6-month-old mice. The ATP-induced current could be abolished reversibly by suramin. Our results suggest that, over the range of developmental stages examined, skeletal muscle cells display an ionotropic purinergic signalling pathway with functional properties qualitatively consistent with what is observed in cultured myotubes. LA - English DB - MTMT ER - TY - JOUR AU - Szentesi, Péter AU - Collet, C AU - Sárközi, Sándor AU - Szegedi, Csaba AU - Jóna, István AU - Jacquemond, V AU - Kovács, László AU - Csernoch, László TI - Effects of dantrolene on steps of excitation-contraction coupling in mammalian skeletal muscle fibers JF - JOURNAL OF GENERAL PHYSIOLOGY J2 - J GEN PHYSIOL VL - 118 PY - 2001 IS - 4 SP - 355 EP - 375 PG - 21 SN - 0022-1295 DO - 10.1085/jgp.118.4.355 UR - https://m2.mtmt.hu/api/publication/1356327 ID - 1356327 N1 - Oct Effects of dantrolene on steps of excitation-contraction coupling in mammalian skeletal muscle fibers AN: ISI:000171535200003 This work was supported by research grants from Hungary (OTKA 030246, 034894, ETT 49/2000, FKFP 0193/2001, and AKP 98-75 3,2/44) and the European Community (CT96-0032). P. Szentesi holds a Bolyai fellowship AB - The effects of the muscle relaxant dantrolene on steps of excitation-contraction coupling were studied on fast twitch muscles of rodents. To identify the site of action of the drug, single fibers for voltage-clamp measurements, heavy SR vesicles for calcium efflux studies and solubilized SR calcium release channels/RYRs for lipid bilayer studies were isolated. Using the double Vaseline-gap or the silicone-clamp technique, dantrolene was found to suppress the depolarization-induced elevation in intracellular calcium concentration ([Ca2+]i) by inhibiting the release of calcium from the SR. The suppression of [Ca2+]i was dose-dependent, with no effect at or below 1 microM and a 53 +/- 8% (mean +/- SEM, n = 9, cut fibers) attenuation at 0 mV with 25 microM of extracellularly applied dantrolene. The drug was not found to be more effective if injected than if applied extracellularly. Calculating the SR calcium release revealed an equal suppression of the steady (53 +/- 8%) and of the early peak component (46 +/- 6%). The drug did not interfere with the activation of the voltage sensor in as much as the voltage dependence of both intramembrane charge movements and the L-type calcium currents (I(Ca)) were left, essentially, unaltered. However, the inactivation of I(Ca) was slowed fourfold, and the conductance was reduced from 200 +/- 16 to 143 +/- 8 SF(-1) (n = 10). Dantrolene was found to inhibit thymol-stimulated calcium efflux from heavy SR vesicles by 44 +/- 10% (n = 3) at 12 microM. On the other hand, dantrolene failed to affect the isolated RYR incorporated into lipid bilayers. The channel displayed a constant open probability for as long as 30-50 min after the application of the drug. These data locate the binding site for dantrolene to be on the SR membrane, but be distinct from the purified RYR itself. LA - English DB - MTMT ER - TY - JOUR AU - Szentesi, Péter AU - Kovács, László AU - Csernoch, László TI - Deterministic inactivation of calcium release channels in mammalian skeletal muscle JF - JOURNAL OF PHYSIOLOGY-LONDON J2 - J PHYSIOL-LONDON VL - 528 PY - 2000 IS - 3 SP - 447 EP - 456 PG - 10 SN - 0022-3751 DO - 10.1111/j.1469-7793.2000.00447.x UR - https://m2.mtmt.hu/api/publication/1356330 ID - 1356330 N1 - Megjegyzés-21018941, ID: 417 Megjegyzés-21116087, ID: 927 ID: 20 AB - Enzymatically dissociated fibres from the extensor digitorum communis muscle of rats were mounted into a double Vaseline gap chamber. The rate of calcium release (R(rel)) from the sarcoplasmic reticulum (SR) and changes in SR permeability to Ca2+ (PSR) were calculated from measured changes in intracellular calcium concentration. Calcium release during a prepulse attenuated the inactivating component of PSR of the subsequent test pulse. The suppression was graded, larger release causing greater suppression, as expected from a calcium-dependent inactivation process. However, if the dissociation constant of the putative inhibitory calcium binding site (Kd) was estimated using different test pulses different affinities were obtained: a smaller test pulse yielded a smaller Kd. Comparing the suppression of the inactivatable component of PSR during the test pulse (suppression) with the inactivatable component during the prepulse (pre-inactivation) revealed a linear relationship with a regression coefficient close to unity. Lowering intracellular magnesium by decreasing its concentration to 25 microM in the internal solution altered the time course of PSR. The maximal peak-to-steady-level ratio was increased to 6.3 +/- 0.4 (n = 10, mean +/- s.e.m.) from a control value of 3.0 +/- 0.2 (n = 19). Despite the apparent change in steady-state inactivation, suppression remained equal to that pre-inactivation. Our results support the view that a depolarizing pulse always recruits the same set of calcium release channels and a portion of these channels undergoes a deterministic inactivation process. LA - English DB - MTMT ER - TY - JOUR AU - Csernoch, László AU - Szentesi, Péter AU - Kovács, László TI - Differential effects of caffeine and perchlorate on excitation-contraction coupling in mammalian skeletal muscle JF - JOURNAL OF PHYSIOLOGY-LONDON J2 - J PHYSIOL-LONDON VL - 520 PY - 1999 IS - 1 SP - 217 EP - 230 PG - 14 SN - 0022-3751 DO - 10.1111/j.1469-7793.1999.00217.x UR - https://m2.mtmt.hu/api/publication/1356336 ID - 1356336 N1 - Megjegyzés-21018556 Oct Differential effects of caffeine and perchlorate on excitation-contraction coupling in mammalian skeletal muscle AN: ISI:000083151900022 PM: PMCID ID: 142; Megjegyzés-21018883, ID: 361; Megjegyzés-21018755, ID: 274; Megjegyzés-21018846, ID: 324; ID: 3 Megjegyzés-21129843, ID: 22; Megjegyzés-21129982, ID: 26; Megjegyzés-21129626, ID: 17; ID: 65 AB - 1. Enzymatically dissociated single muscle fibres of the rat were studied under voltage clamp conditions in a double Vaseline gap experimental chamber. Intramembrane charge movement and changes in intracellular calcium concentration ([Ca2+]i) were measured and the rate of calcium release (Rrel) from the sarcoplasmic reticulum (SR) was calculated. This enabled the determination of SR permeability and thus the estimation of the transfer function between intramembrane charge movement and SR permeability. 2. Perchlorate (3 mM) shifted the membrane potential dependence of intramembrane charge movement to more negative voltages without any effect on the steepness or on the maximal available charge. The drug increased SR permeability at every membrane potential but did not alter the peak-to-steady level ratio. It also increased the slope of the transfer function, indicating a more efficient coupling between the voltage sensors and the ryanodine receptors. 3. Caffeine (1 mM), on the other hand, increased SR permeability without altering the voltage dependence of intramembrane charge movement. It neither prolonged the depolarization-induced increase in [Ca2+]i at short pulse durations nor altered the time to peak of Rrel. The augmentation of SR permeability by the drug was more pronounced during the peak caffeine response than during its steady level. This was manifested in a leftward shift of the transfer function rather than an increase in its slope. 4. These observations indicate that perchlorate and caffeine alter the coupling between the voltage sensors and SR calcium release channels in mammalian skeletal muscle. They do not, however, share a common mechanism for enhancing the depolarization-induced release of calcium from the SR. LA - English DB - MTMT ER - TY - JOUR AU - Csernoch, László TI - Regulation of the ryanodine receptor calcium release channel of the sarcoplasmic reticulum in skeletal muscle JF - ACTA PHYSIOLOGICA HUNGARICA J2 - ACTA PHYSIOL HUNG VL - 86 PY - 1999 IS - 2 SP - 77 EP - 97 PG - 21 SN - 0231-424X UR - https://m2.mtmt.hu/api/publication/237046 ID - 237046 AB - In striated muscle contraction is under the tight control of myoplasmic calcium concentration ([Ca2+](i)): the elevation in [Ca2+](i) and the consequent binding of calcium to troponin C enables, while the decrease in [Ca2+](i) prevents the actin-myosin interaction. Calcium ions at rest are stored in the sarcoplasmic reticulum (SR) from which they are rapidly released upon the depolarisation of the sarcolemmal and transverse (T-) tubular membranes of the muscle cell. The protein responsible for this controlled and fast release of calcium is the calcium release channel found in the membrane of the terminal cisternae of the SR. This review focuses on the physiological and pharmacological modulators of the calcium release channel and tries to draw an up-to-date picture of the events that occur between T-tubular depolarisation and the release of calcium from the SR. LA - English DB - MTMT ER - TY - JOUR AU - Szentesi, Péter AU - Jacquemond, Vincent AU - Kovács, László AU - Csernoch, László TI - Intramembrane charge movement and sarcoplasmic calcium release in enzymatically isolated mammalian skeletal muscle fibres JF - JOURNAL OF PHYSIOLOGY-LONDON J2 - J PHYSIOL-LONDON VL - 505 PY - 1997 IS - 2 SP - 371 EP - 384 PG - 14 SN - 0022-3751 DO - 10.1111/j.1469-7793.1997.371bb.x UR - https://m2.mtmt.hu/api/publication/1356341 ID - 1356341 N1 - Dec Intramembrane charge movement and sarcoplasmic calcium release in enzymatically isolated mammalian skeletal muscle fibres AN: ISI:000071076600010 PM: PMCID ID: 283 AB - 1. Single muscle fibres were dissociated enzymatically from the extensor digitorum longus and communis muscles of rats and guinea-pigs. The fibres were mounted into a double Vaseline gap experimental chamber and the events in excitation-contraction coupling were studied under voltage clamp conditions. 2. The voltage dependence of intramembrane charge movement followed a two-state Boltzmann distribution with maximal available charge of 26.1 +/- 1.5 and 26.1 +/- 1.3 nC microF-1, mid-point voltage of -35.1 +/- 5.0 and -42.2 +/- 1.2 mV and steepness of 16.7 +/- 2.2 and 17.0 +/- 1.9 mV (means +/- S.E.M., n = 7 and 4) in rats and guinea-pigs, respectively. 3. Intracellular calcium concentration ([Ca2+]i) was monitored using the calcium-sensitive dyes antipyrylazo III, fura-2 and mag-fura-5. Resting [Ca2+]i was similar in rats and guinea-pigs with 125 +/- 18 and 115 +/- 8 nM (n = 10 and 9), respectively, while the maximal increase for a 100 ms depolarization to 0 mV was larger in rats (6.3 +/- 1.0 microM; n = 7), than in guinea-pigs (2.8 +/- 0.3; n = 4). 4. The rate of calcium release (Rrel) from the sarcoplasmic reticulum (SR) displayed an early peak followed by a fast and a slow decline to a quasi maintained steady level. After normalizing Rrel to the estimated SR calcium content (1.2 +/- 0.1 and 0.9 +/- 0.1 mM in rats and guinea-pigs, respectively) and correcting for depletion of calcium in the SR the peak and steady levels at 0 mV, respectively, were found to be 2.50 +/- 0.08 and 0.81 +/- 0.06% ms-1 in rats and 2.43 +/- 0.25 and 0.88 +/- 0.01% ms-1 in guinea-pigs. The voltage dependence was essentially the same in both species, but different from that in amphibians. 5. These experiments show that enzymatic isolation yields functionally intact mammalian skeletal muscle fibres for Vaseline gap experiments. The data also suggest a close connection in the regulation of the different kinetic components of SR calcium release in mammalian skeletal muscle. LA - English DB - MTMT ER - TY - JOUR AU - Csernoch, László AU - Jacquemond, V AU - Schneider, M F TI - Microinjection of strong calcium buffers suppresses the peak of calcium release during depolarization in frog skeletal muscle fibers JF - JOURNAL OF GENERAL PHYSIOLOGY J2 - J GEN PHYSIOL VL - 101 PY - 1993 IS - 2 SP - 297 EP - 333 PG - 37 SN - 0022-1295 DO - 10.1085/jgp.101.2.297 UR - https://m2.mtmt.hu/api/publication/1356344 ID - 1356344 N1 - Megjegyzés-21018714 Feb MICROINJECTION OF STRONG CALCIUM BUFFERS SUPPRESSES THE PEAK OF CALCIUM RELEASE DURING DEPOLARIZATION IN FROG SKELETAL-MUSCLE FIBERS AN: ISI:A1993KM87100006 PM: PMCID ID: 254 Megjegyzés-21130019, ID: 74 Megjegyzés-21129862, ID: 43 ID: 117 AB - The effects of high intracellular concentrations of various calcium buffers on the myoplasmic calcium transient and on the rate of release of calcium (Rrel) from the sarcoplasmic reticulum (SR) were studied in voltage-clamped frog skeletal muscle fibers. The changes in intracellular calcium concentration (delta[Ca2+]) for 200-ms pulses to 0-20 mV were recorded before and after the injection of the calcium buffer and the underlying Rrel was calculated. If the buffer concentration after the injection was high, the initial rate of rise of the calcium transient was slower after injection than before and was followed by a slow increase of [Ca2+] that resembled a ramp. The increase in myoplasmic [Mg2+] that accompanies the calcium transient in control was suppressed after the injection and a slight decrease was observed instead. After the injection the buffer concentration in the voltage-clamped segment of the fiber decreased as the buffer diffused away toward the open ends. The calculated apparent diffusion coefficient for fura-2 (Dapp = 0.40 +/- 0.03 x 10(-6) cm2/s, mean +/- SEM, n = 6) suggests that approximately 65-70% of the indicator was bound to relatively immobile intracellular constituents. As the concentration of the injected buffer decreased, the above effects were reversed. The changes in delta[Ca2+] were underlined by characteristic modification of Rrel. The early peak component was suppressed or completely eliminated; thus, Rrel rose monotonically to a maintained steady level if corrected for depletion. If Rrel was expressed as percentage of SR calcium content, the steady level after injection did not differ significantly from that before. Control injections of anisidine, to the concentration that eliminated the peak of Rrel when high affinity buffers were used, had only a minor effect on Rrel, the peak was suppressed by 26 +/- 5% (mean +/- SE, n = 6), and the steady level remained unchanged. Thus, the peak component of Rrel is dependent on a rise in myoplasmic [Ca2+], consistent with calcium-induced calcium release, whereas the steady component of Rrel is independent of myoplasmic [Ca2+]. LA - English DB - MTMT ER - TY - JOUR AU - Pizarro, G AU - Csernoch, László AU - Uribe, I AU - Rios, E TI - Differential effects of tetracaine on two kinetic components of calcium release in frog skeletal muscle fibres JF - JOURNAL OF PHYSIOLOGY-LONDON J2 - J PHYSIOL-LONDON VL - 457 PY - 1992 SP - 525 EP - 538 PG - 14 SN - 0022-3751 UR - https://m2.mtmt.hu/api/publication/1356345 ID - 1356345 N1 - Megjegyzés-21130086 Nov DIFFERENTIAL-EFFECTS OF TETRACAINE ON 2 KINETIC COMPONENTS OF CALCIUM RELEASE IN FROG SKELETAL-MUSCLE FIBERS AN: ISI:A1992JY70500031 PM: PMCID ID: 12 Megjegyzés-21018599, ID: 185 Megjegyzés-21116119, ID: 959 Megjegyzés-21129870, ID: 45 ID: 118 AB - 1. Intramembrane charge movements and changes in intracellular calcium concentration were recorded simultaneously in voltage clamped cut skeletal muscle fibres of the frog in the presence and absence of tetracaine. 2. Extracellular application of 20 microM tetracaine reduced the increase in myoplasmic [Ca2+]. The effect on the underlying calcium release flux from the sarcoplasmic reticulum was to suppress the peak of the release while sparing the steady level attained at the end of 100 ms clamp depolarizations. 3. While the peak of the release flux at corresponding voltages was reduced by 62% after the addition of tetracaine, the rate of inactivation was the same when the pulses elicited release fluxes of similar amplitude. 4. Higher concentrations of tetracaine, 0.2 mM, abolished the calcium signal in stretched fibres whereas in slack fibres this concentration left a non-inactivating calcium release flux. 5. Lowering the extracellular pH antagonized the effect of the drug both on charge movements and on calcium signals. The permanently charged analogue tetracaine methobromide lacked effects on excitation-contraction coupling. 6. These results imply that the two kinetic components of calcium release flux have very different tetracaine sensitivities. They are also consistent with an intracellular site of action of the drug at low concentration. Taken together they strongly suggest that the inactivating and non-inactivating components of calcium release correspond to different pathways: one that inactivates, is sensitive to tetracaine and is controlled by calcium, and another that does not inactivate, is much less sensitive to tetracaine and is directly controlled by voltage. LA - English DB - MTMT ER - TY - JOUR AU - Szűcs, Géza AU - Papp, Zoltán AU - Csernoch, László AU - Kovács, László TI - KINETIC-PROPERTIES OF INTRAMEMBRANE CHARGE MOVEMENT UNDER DEPOLARIZED CONDITIONS IN FROG SKELETAL-MUSCLE FIBERS JF - JOURNAL OF GENERAL PHYSIOLOGY J2 - J GEN PHYSIOL VL - 98 PY - 1991 IS - 2 SP - 365 EP - 378 PG - 14 SN - 0022-1295 DO - 10.1085/jgp.98.2.365 UR - https://m2.mtmt.hu/api/publication/1407689 ID - 1407689 N1 - Aug KINETIC-PROPERTIES OF INTRAMEMBRANE CHARGE MOVEMENT UNDER DEPOLARIZED CONDITIONS IN FROG SKELETAL-MUSCLE FIBERS AN: ISI:A1991GA94500007 PM: PMCID ID: 36 Megjegyzés-21129808, ID: 28 Megjegyzés-21130092, ID: 17 Megjegyzés-21129669, ID: 60 ID: 41 AB - Intramembrane charge movement was measured on skeletal muscle fibers of the frog in a single Vaseline-gap voltage clamp. Charge movements determined both under polarized conditions (holding potential, VH = -100 mV; Qmax = 30.4 +/- 4.7 nC/micro(F), V = -44.4 mV, k = 14.1 mV; charge 1) and in depolarized states (VH = 0 mV; Qmax = 50.0 +/- 6.7 nC/micro(F), V = -109.1 mV, k = 26.6 mV; charge 2) had properties as reported earlier. Linear capacitance (LC) of the polarized fibers was increased by 8.8 +/- 4.0% compared with that of the depolarized fibers. Using control pulses measured under depolarized conditions to calculate charge 1, a minor change in the voltage dependence (to V = -44.6 mV and k = 14.5 mV) and a small increase in the maximal charge (to Qmax = 31.4 +/- 5.5 nC/micro(F] were observed. While in most cases charge 1 transients seemed to decay with a single exponential time course, charge 2 currents showed a characteristic biexponential behavior at membrane potentials between -90 and -180 mV. The voltage dependence of the rate constant of the slower component was fitted with a simple constant field diffusion model (alpha m = 28.7 s-1, V = -124.0 mV, and k = 15.6 mV). The midpoint voltage (V) was similar to that obtained from the Q-V fit of charge 2, while the steepness factor (k) resembled that of charge 1. This slow component could also be isolated using a stepped OFF protocol; that is, by hyperpolarizing the membrane to -190 mV for 200 ms and then coming back to 0 mV in two steps. The faster component was identified as an ionic current insensitive to 20 mM Co2+ but blocked by large hyperpolarizing pulses. These findings are consistent with the model implying that charge 1 and the slower component of charge 2 interconvert when the holding potential is changed. They also explain the difference previously found when comparing the steepness factors of the voltage dependence of charge 1 and charge 2. LA - English DB - MTMT ER -