scholarly journals Longitudinal Impedance of Skinned Frog Muscle Fibers

1974 ◽  
Vol 63 (5) ◽  
pp. 625-638 ◽  
Author(s):  
Bert A. Mobley ◽  
J. Leung ◽  
R. S. Eisenberg
Keyword(s):  
Muscle Fibers ◽  
Longitudinal Section ◽  
Skinned Fibers ◽  
Stray Capacitance ◽  
Chemical Methods ◽  
Semitendinosus Muscle ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers ◽  
Longitudinal Impedance ◽  
Zero Phase

Longitudinal impedance of skinned muscle fibers was measured with extracellular electrodes and an oil gap method in which a central longitudinal section of fiber is insulated by oil while the ends of the fiber are bathed in conducting pools of relaxing solution. Intact single fibers were isolated from frog semitendinosus muscle and the sarcolemma removed either by mechanical or chemical methods. Stray capacitance across the oil gap was measured after each experiment and its admittance subtracted from the admittance of the fiber and oil gap. Effects of impedance at the ends of the fiber were eliminated by measuring the impedance with two lengths of fiber in the oil gap and subtracting the impedance at the shorter length from that at the longer length. Longitudinal impedance so determined for mechanically and chemically skinned fibers exhibited zero phase shift from 1 to 10,000 Hz, i.e., the longitudinal impedance of skinned fibers is purely resistive. If we assume that our skinned fibers are a model of the sarcoplasm of muscle, we conclude that the equivalent circuit of the sarcoplasm is a resistor.

scholarly journals Excitation of skinned muscle fibers by imposed ion gradients. II. Influence of quercetin and ATP removal on the Ca2+-insensitive component of stimulated 45Ca efflux.

1985 ◽  
Vol 86 (6) ◽  
pp. 833-852 ◽  
Author(s):  
E W Stephenson
Keyword(s):  
Adenine Nucleotide ◽  
Isometric Force ◽  
Muscle Fibers ◽  
Semitendinosus Muscle ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers ◽  
Unstimulated Control ◽  
Dependent Component ◽  
Control Loss ◽  
45Ca Efflux

Ionic gradients imposed by choline Cl replacement of K methanesulfonate (Mes) at constant [K][Cl] product stimulate 45Ca efflux from skinned muscle fibers; a small, sustained Ca2+-insensitive efflux component, observed in EGTA, appears to grade a much larger Ca2+-dependent component responsible for contractile activation and is likely to reflect intermediate steps in excitation-contraction coupling. The present studies examined ATP-related effects on the Ca2+-insensitive stimulation. 45Ca efflux was measured on segments of frog semitendinosus muscle skinned by microdissection, with isometric force monitored continuously. The Ca2+-insensitive component was potentiated by quercetin, a flavonoid thought to inhibit the sarcoplasmic reticulum (SR) Ca pump by stabilizing a phosphorylated intermediate. Quercetin increased the stimulated net 45Ca release in the absence of EGTA, as expected from inhibition of reaccumulation, but its effectiveness in EGTA indicated potentiation of unidirectional efflux as such. Quercetin also increased unstimulated (control) 45Ca efflux in EGTA, to a smaller extent; potentiation appeared to be a function of efflux, with stimulation above control loss increased approximately 2.6-fold. ATP removal before stimulation, which led to rigor force and increased stiffness, prevented all quercetin effects in EGTA. ATP removal by itself inhibited ionic stimulation of the Ca2+-insensitive component, with little residual increase above the parallel control loss. Addition of the nonhydrolyzable ATP analogue AMP-PCP ([adenylyl-beta,gamma-methylene]diphosphate) (0.8 mM) after ATP removal gave similar results to ATP-free solution, which suggests that adenine nucleotide binding alone does not support stimulation by choline Cl. These results imply a fundamental role for ATP in the excitation of skinned fibers by imposed diffusion potentials; they also suggest that ATP regulates the SR Ca efflux channel, in a manner that could provide the positive feedback in Ca2+-dependent Ca release.

scholarly journals Influence of magnesium on chloride-induced calcium release in skinned muscle fibers.

1977 ◽  
Vol 69 (1) ◽  
pp. 17-35 ◽  
Author(s):  
E W Stephenson ◽  
R J Podolsky
Keyword(s):  
Calcium Release ◽  
Isometric Force ◽  
Muscle Fibers ◽  
Ringer Solution ◽  
Skinned Fibers ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers ◽  
Ca Uptake ◽  
45Ca Release ◽  
Net Release

Chloride-induced Ca release in skinned muscle fibers was studied by measuring isometric force transients and 45Ca loss from fiber to washout solutions. Skinned fibers prepared from muscles soaked in normal Ringer solution made large force transients in 120 mM Cl solution with 5 mM ATP and 1 mM Mg, but 3 mM Mg was inhibitory. Mg inhibition was antagonized by low temperature and by Cd, agents which slow active Ca uptake by the sarcoplasmic reticulum (SR). In low Mg++, Cl stimulated rapid 45Ca release from the SR in sufficient amounts to account for the force response. The increased 45Ca release was inhibited by EGTA, suggesting that release requires free Ca under these conditions. The 45Ca initially released was partially reaccumulated later. Reaccumulation was increased in higher Mg++. These results provide additional evidence that the Ca uptake rate is an important determinant of net release, and suggest that Mg++ acts primarily on this mechanism. Skinned fibers prepared from muscles soaked in low Cl solutions could give force responses to Cl solutions with 3 mM and 6 mM Mg. This observation suggests that the Cl stimulus varies with the [Cl] gradient across the internal membranes, and supports the hypothesis that applied Cl causes membrane depolarization.

scholarly journals Excitation of skinned muscle fibers by imposed ion gradients. I. Stimulation of 45Ca efflux at constant [K][Cl] product.

1985 ◽  
Vol 86 (6) ◽  
pp. 813-832 ◽  
Author(s):  
E W Stephenson
Keyword(s):  
Isometric Force ◽  
Muscle Fibers ◽  
Water Flux ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers ◽  
Diffusion Potentials ◽  
45Ca Efflux ◽  
Osmotic Effects ◽  
45Ca Release ◽  
And Diffusion

45Ca efflux from skinned muscle fibers is stimulated transiently, by a highly Ca2+-dependent mechanism, by KCl replacement of K propionate. In the present studies, Cl replaced the much less permeant anion methanesulfonate (Mes) either (a) at constant [K], in which increased [K][Cl] permits net KCl and water flux across internal membranes, or (b) at constant [K][Cl] (choline substitution), in which the imposed gradients and diffusion potentials should dissipate slowly. 45Ca efflux and isometric force were measured simultaneously on segments of frog semitendinosus fibers skinned by microdissection. EGTA was applied to chelate released 45Ca either (a) shortly after high [Cl] (interrupted response), to minimize reaccumulation, (b) before high [Cl] (pretreated response), to evaluate Ca2+ dependence, or (c) under control conditions in KMes. KCl replacement of KMes stimulated release of 65% fiber 45Ca within 1 min in interrupted responses; EGTA pretreatment was only moderately inhibitory with substantial residual stimulation. In contrast, choline Cl replacement of KMes induced release of 26-35% fiber 45Ca in interrupted responses; EGTA pretreatment was strongly inhibitory, but release significantly exceeded control with a small, sustained increase in Ca2+-insensitive efflux. These differences in 45Ca release and EGTA inhibition suggest that Cl replacement of Mes at constant [K] stimulates efflux by osmotic effects as well as imposed diffusion potentials; at least half the stimulated 45Ca loss (above control) in interrupted KCl responses is attributable to an osmotic component with low Ca2+ sensitivity. In the highly Ca2+-sensitive stimulation at constant [K][Cl], 45Ca release (above control) in interrupted responses correlated well with that in the pretreated responses of segments from the same fiber, with a slope of 8.4. This relationship suggests that imposed diffusion potentials stimulate a small Ca2+-insensitive component that gradates a much larger Ca2+-dependent efflux. The Ca2+-insensitive component apparently reflects intermediate steps in the excitation-contraction coupling that require positive feedback to result in sufficient Ca release for contraction.

Enhancement of Ca2+-induced Ca2+ release in calpain treated rabbit skinned muscle fibers

1992 ◽  
Vol 185 (2) ◽  
pp. 713-718 ◽  
Author(s):  
Masamitsu Iino ◽  
Hiromi Takano-Ohmuro ◽  
Yoko Kawana ◽  
Makoto Endo
Keyword(s):  
Muscle Fibers ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers
Sign in / Sign up

Export Citation Format

Share Document