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. 1982;324:297–318. doi: 10.1113/jphysiol.1982.sp014114

Activation and inactivation characteristics of the sodium permeability in muscle fibres from Rana temporaria

Carol A Collins 1,*, E Rojas 1, B A Suarez-Isla 1,†
PMCID: PMC1250707  PMID: 6980273

Abstract

1. The steady-state and kinetic characteristics of the processes of activation and inactivation of the Na+ permeability, PNa, were measured in cut skeletal muscle fibres from Rana temporaria under voltage-clamp conditions.

2. The specific resistance, rss, in series with the surface sarcolemma, was estimated as 6 Ω cm2 by measuring the initial value of the membrane potential transient in response to current pulses under current-clamp conditions. To reduce the error in the potential across the sarcolemma introduced by rss, Na+ currents were recorded using positive feed-back compensation, in the presence of tetrodotoxin (2·4-5 nm).

3. PNa(t) was fitted with m3h kinetics assuming a voltage-dependent delay, δt, to the start of the activation process.

4. The PNa—Vp curve exhibited saturation at potentials more positive than 30 mV. m∞, calculated as (PNa, ∞/¯PNa)⅓ as a function of Vp, was a sigmoid curve with a mid point at -35 mV. The slope, dm∞/dVp, at this point was 0·032 mV-1.

5. Using a double-pulse protocol a non-exponential time course for the development of fast inactivation at small depolarizations was observed.

6. The time constant for activation, τm, as a function of Vp, and τh as a function of Vp, could be fitted with an approximately bell-shaped function, maximum of 430 μs at -43 mV and 925 μs at -78 mV respectively, at 15 °C.

7. The mid-point potential of the h∞—Vl curve occurred at -58 mV, and h∞ approached 1 for V1 values more negative than -103 mV.

8. Using a double-pulse procedure the development of a slow inactivation of the Na+ current was demonstrated. Its time course could be described in terms of a single exponential function, time constant equal to 0·58 s. The recovery from slow inactivation could be described by a similar exponential for recovery times smaller than 1 s.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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