A quantitative description of the voltage-dependent capacitance in frog skeletal muscle in terms of equilibrium statistical mechanics

1982 ◽  
Vol 215 (1198) ◽  
pp. 75-94 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Statistical Mechanics ◽  
Applied Voltage ◽  
Energy Levels ◽  
Quantitative Description ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Free Energies ◽  
Equilibrium Statistical Mechanics ◽  
Charge Movements

We present an analysis of experimental steady-state properties of charge movements in voltage-clamped frog skeletal muscle; by adopting an approach based on equilibrium statistical mechanics, detailed assumptions about the dynamics of the charge movement were avoided. Different components of the charge movements, as characterized by their sensitivities to local anaesthetics, were taken to correspond to different types of independent subsystem (integral membrane proteins). Quantitative agreement with the data for the q β and q γ components was obtained for the simplest subsystems, having two energy levels; however, q α required three (or more) energy levels. Each of the subsystems can be interpreted as having a charged group, minimum valency z , able to occupy two or more positions within the membrane. The tetracaine-sensitive q γ charge can be described in terms of an ensemble of subsystems having z = 4.5, each occupying one of two levels whose free energies at zero applied voltage differ by 1.7 x 10 -1 eV. Likewise, the lidocaine-sensitive q β has z = 1.0, free energy difference 1.9 x 10 -2 eV. However, the simplest model for the lidocaine-resistant q α involves a charge of valency 1.7 moving between three levels having relative free energies at zero applied voltage — 9.7 x 10 -2 , 0, and 2.1 x 10 -2 eV respectively, where the intermediate level ‘ sees ’ about 50 % of the applied voltage.

scholarly journals Sodium channel gating currents in frog skeletal muscle.

1983 ◽  
Vol 82 (5) ◽  
pp. 679-701 ◽  
Author(s):  
D T Campbell
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Time Course ◽  
Channel Gating ◽  
Total Charge ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Gating Currents ◽  
Gating Mechanism ◽  
Charge Movements

Charge movements similar to those attributed to the sodium channel gating mechanism in nerve have been measured in frog skeletal muscle using the vaseline-gap voltage-clamp technique. The time course of gating currents elicited by moderate to strong depolarizations could be well fitted by the sum of two exponentials. The gating charge exhibits immobilization: at a holding potential of -90 mV the proportion of charge that returns after a depolarizing prepulse (OFF charge) decreases with the duration of the prepulse with a time course similar to inactivation of sodium currents measured in the same fiber at the same potential. OFF charge movements elicited by a return to more negative holding potentials of -120 or -150 mV show distinct fast and slow phases. At these holding potentials the total charge moved during both phases of the gating current is equal to the ON charge moved during the preceding prepulse. It is suggested that the slow component of OFF charge movement represents the slower return of charge "immobilized" during the prepulse. A slow mechanism of charge immobilization is also evident: the maximum charge moved for a strong depolarization is approximately doubled by changing the holding potential from -90 to -150 mV. Although they are larger in magnitude for a -150-mV holding potential, the gating currents elicited by steps to a given potential have similar kinetics whether the holding potential is -90 or -150 mV.

scholarly journals Differential effects of tetracaine on charge movements and Ca2+ signals in frog skeletal muscle.

1988 ◽  
Vol 92 (5) ◽  
pp. 601-612 ◽  
Author(s):  
L Csernoch ◽  
C L Huang ◽  
G Szucs ◽  
L Kovacs
Keyword(s):  
Skeletal Muscle ◽  
Charge Transfer ◽  
Calcium Release ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Semitendinosus Muscle ◽  
Contraction Coupling ◽  
Low Concentrations ◽  
Myofilament Activation ◽  
Charge Movements

The effects of tetracaine on charge movements and on antipyrylazo III signals monitoring intracellular delta [Ca2+] were compared in cut frog semitendinosus muscle fibers in a single vaseline gap-voltage clamp. Low tetracaine concentrations (25-40 microM) markedly reduced delta [Ca2+] signals and shifted the rheobase. However, they neither influenced charge movement nor that peak delta [Ca2+] value associated with the contractile threshold. Higher tetracaine concentrations (100-200 microM) partly inhibited charge movements in cut fibers. They separated a steeply voltage-sensitive charge, some of whose features resembled 'q gamma' reported in intact fibers, and whose movement preceded delta [Ca2+] signals at threshold. These findings: (a) directly confirm an earlier suggestion that tetracaine acts on steps in excitation-contraction coupling rather than myofilament activation; (b) show that tetracaine at low concentrations can directly interfere with sarcoplasmic reticular calcium release without modifying charge movement; (c) show that the tetracaine-sensitive charge, first found in intact fibers, also exists in cut fibers; and (d) make it unlikely that tetracaine-sensitive charge transfer is a consequence of Ca2+ release as suggested on earlier occasions.

scholarly journals Anatomical distribution of voltage-dependent membrane capacitance in frog skeletal muscle fibers.

1989 ◽  
Vol 93 (3) ◽  
pp. 565-584 ◽  
Author(s):  
C L Huang ◽  
L D Peachey
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Fiber Surface ◽  
Membrane Capacitance ◽  
Hypertonic Solution ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Transverse Tubule ◽  
Skeletal Muscle Fibers ◽  
Voltage Dependent

Components of nonlinear capacitance, or charge movement, were localized in the membranes of frog skeletal muscle fibers by studying the effect of 'detubulation' resulting from sudden withdrawal of glycerol from a glycerol-hypertonic solution in which the muscles had been immersed. Linear capacitance was evaluated from the integral of the transient current elicited by imposed voltage clamp steps near the holding potential using bathing solutions that minimized tubular voltage attenuation. The dependence of linear membrane capacitance on fiber diameter in intact fibers was consistent with surface and tubular capacitances and a term attributable to the capacitance of the fiber end. A reduction in this dependence in detubulated fibers suggested that sudden glycerol withdrawal isolated between 75 and 100% of the transverse tubules from the fiber surface. Glycerol withdrawal in two stages did not cause appreciable detubulation. Such glycerol-treated but not detubulated fibers were used as controls. Detubulation reduced delayed (q gamma) charging currents to an extent not explicable simply in terms of tubular conduction delays. Nonlinear membrane capacitance measured at different voltages was expressed normalized to accessible linear fiber membrane capacitance. In control fibers it was strongly voltage dependent. Both the magnitude and steepness of the function were markedly reduced by adding tetracaine, which removed a component in agreement with earlier reports for q gamma charge. In contrast, detubulated fibers had nonlinear capacitances resembling those of q beta charge, and were not affected by adding tetracaine. These findings are discussed in terms of a preferential localization of tetracaine-sensitive (q gamma) charge in transverse tubule membrane, in contrast to a more even distribution of the tetracaine-resistant (q beta) charge in both transverse tubule and surface membranes. These results suggest that q beta and q gamma are due to different molecules and that the movement of q gamma in the transverse tubule membrane is the voltage-sensing step in excitation-contraction coupling.

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