scholarly journals Kinetic and pharmacological properties of the sodium channel of frog skeletal muscle.

1976 ◽  
Vol 67 (3) ◽  
pp. 309-323 ◽  
Author(s):  
D T Campbell ◽  
B Hille
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Dissociation Constants ◽  
Quantitative Description ◽  
Potential Drop ◽  
Na Channels ◽  
Frog Skeletal Muscle ◽  
Myelinated Nerve ◽  
Sodium Permeability ◽  
Block Of Na Channels

Na channels of frog skeletal muscle are studied under voltage clamp and their properties compared with those of frog myelinated nerve. A standard mathematical model is fitted to the sodium currents measured in nerve and in muscle to obtain a quantitative description of the gating kinetics. At 5 degrees C the kinetics in frog nerve and skeletal muscle are similar except that activation proceeds five times faster in nerve. Block of Na channels by saxitoxin is measured in nerve and in muscle. The apparent dissociation constants for the inhibitory complex are about 1 nM and not significantly different in nerve and muscle. Block of Na channels by external protons in muscle is found to have an apparent pKalpha of 5.33 and a voltage dependence corresponding to action of 27% of the membrane potential drop. Both values are like those for nerve. Shift of the peak sodium permeability-membrane potential curve with changes of external pH and Ca++ are found to be the same in nerve and muscle. It is concluded that Na channels of nerve and muscle are nearly the same.

scholarly journals Relationships between resting conductances, excitability, and t-system ionic homeostasis in skeletal muscle

2011 ◽  
Vol 138 (1) ◽  
pp. 95-116 ◽  
Author(s):  
James A. Fraser ◽  
Christopher L.-H. Huang ◽  
Thomas H. Pedersen
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Conduction Velocity ◽  
Electrical Response ◽  
Quantitative Description ◽  
Ion Concentration ◽  
Ionic Homeostasis ◽  
Voltage Gated ◽  
Concentration Changes ◽  
T System

Activation of skeletal muscle fibers requires rapid sarcolemmal action potential (AP) conduction to ensure uniform excitation along the fiber length, as well as successful tubular excitation to initiate excitation–contraction coupling. In our companion paper in this issue, Pedersen et al. (2011. J. Gen. Physiol. doi:10.1085/jgp.201010510) quantify, for subthreshold stimuli, the influence upon both surface conduction velocity and tubular (t)-system excitation of the large changes in resting membrane conductance (GM) that occur during repetitive AP firing. The present work extends the analysis by developing a multi-compartment modification of the charge–difference model of Fraser and Huang to provide a quantitative description of the conduction velocity of actively propagated APs; the influence of voltage-gated ion channels within the t-system; the influence of t-system APs on ionic homeostasis within the t-system; the influence of t-system ion concentration changes on membrane potentials; and the influence of Phase I and Phase II GM changes on these relationships. Passive conduction properties of the novel model agreed with established linear circuit analysis and previous experimental results, while key simulations of AP firing were tested against focused experimental microelectrode measurements of membrane potential. This study thereby first quantified the effects of the t-system luminal resistance and voltage-gated Na+ channel density on surface AP propagation and the resultant electrical response of the t-system. Second, it demonstrated the influence of GM changes during repetitive AP firing upon surface and t-system excitability. Third, it showed that significant K+ accumulation occurs within the t-system during repetitive AP firing and produces a baseline depolarization of the surface membrane potential. Finally, it indicated that GM changes during repetitive AP firing significantly influence both t-system K+ accumulation and its influence on the resting membrane potential. Thus, the present study emerges with a quantitative description of the changes in membrane potential, excitability, and t-system ionic homeostasis that occur during repetitive AP firing in skeletal muscle.

scholarly journals Strophanthidin-sensitive sodium fluxes in metabolically poisoned frog skeletal muscle.

1976 ◽  
Vol 68 (4) ◽  
pp. 405-420 ◽  
Author(s):  
B G Kennedy ◽  
P De Weer
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Human Erythrocyte ◽  
Sodium Pump ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Frog Skeletal Muscle ◽  
Na Efflux ◽  
Unidirectional Fluxes ◽  
External K

Strophanthidin-sensitive and insensitive unidirectional fluxes of Na were measured in fog sartorius muscles whose internal Na levels were elevated by overnight storage in the cold. ATP levels were lowered, and ADP levels raised, by metabolic poisoning with either 2,4-dinitrofluorobenzene or iodoacetamide. Strophanthidin-sensitive Na efflux and influx both increased after poisoning, while strophanthidin-insensitives fluxes did not. The increase in efflux did not require the presence of external K but was greatly attenuated when Li replaced Na as the major external cation. Membrane potential was not markedly altered by 2,4-dinitrofluorobenzene. These observations indicate that the sodium pump of frog skeletal muscle resembles that of squid giant axon and human erythrocyte in its ability to catalyze Na-Na exchange to an extent determined by intracellular ATP/ADP levels.

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 Myoplasmic calcium transients in intact frog skeletal muscle fibers monitored with the fluorescent indicator furaptra.

1991 ◽  
Vol 97 (2) ◽  
pp. 271-301 ◽  
Author(s):  
M Konishi ◽  
S Hollingworth ◽  
A B Harkins ◽  
S M Baylor
Keyword(s):  
Skeletal Muscle ◽  
Time Course ◽  
Dissociation Constants ◽  
Diffusion Constant ◽  
Preceding Paper ◽  
Excitation Wavelength ◽  
Frog Skeletal Muscle ◽  
Fluorescent Indicator ◽  
Single Action

Furaptra (Raju, B., E. Murphy, L. A. Levy, R. D. Hall, and R. E. London. 1989. Am. J. Physiol. 256:C540-C548) is a "tri-carboxylate" fluorescent indicator with a chromophore group similar to that of fura-2 (Grynkiewicz, G., M. Poenie, and R. Y. Tsien. 1985. J. Biol. Chem. 260:3440-3450). In vitro calibrations indicate that furaptra reacts with Ca2+ and Mg2+ with 1:1 stoichiometry, with dissociation constants of 44 microM and 5.3 mM, respectively (16-17 degrees C; ionic strength, 0.15 M; pH, 7.0). Thus, in a frog skeletal muscle fiber stimulated electrically, the indicator is expected to respond to the change in myoplasmic free [Ca2+] (delta[Ca2+]) with little interference from changes in myoplasmic free [Mg2+]. The apparent longitudinal diffusion constant of furaptra in myoplasm was found to be 0.68 (+/- 0.02, SEM) x 10(-6) cm2 s-1 (16-16.5 degrees C), a value which suggests that about half of the indicator was bound to myoplasmic constituents of large molecular weight. Muscle membranes (surface and/or transverse-tubular) appear to have some permeability to furaptra, as the total quantity of indicator contained within a fiber decreased after injection; the average time constant of the loss was 302 (+/- 145, SEM) min. In fibers containing less than 0.5 mM furaptra and stimulated by a single action potential, the calibrated peak value of delta[Ca2+] averaged 5.1 (+/- 0.3, SEM) microM. This value is about half that reported in the preceding paper (9.4 microM; Konishi, M., and S. M. Baylor. 1991. J. Gen. Physiol. 97:245-270) for fibers injected with purpurate-diacetic acid (PDAA). The latter difference may be explained, at least in part, by the likelihood that the effective dissociation constant of furaptra for Ca2+ is larger in vivo than in vitro, owing to the binding of the indicator to myoplasmic constituents. The time course of furaptra's delta[Ca2+], with average values (+/- SEM) for time to peak and half-width of 6.3 (+/- 0.1) and 9.5 (+/- 0.4) ms, respectively, is very similar to that of delta[Ca2+] recorded with PDAA. Since furaptra's delta[Ca2+] can be recorded at a single excitation wavelength (e.g., 420 nm) with little interference from fiber intrinsic changes, movement artifacts, or delta[Mg2+], furaptra represents a useful myoplasmic Ca2+ indicator, with properties complementary to those of other available indicators.

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