Kinetics of Na inactivation in frog atria

Autor: H. M. Einwächter, R. Kern, H. G. Haas, M. Tarr
Rok vydání: 1971
Předmět:
Zdroj: Pfl�gers Archiv European Journal of Physiology. 323:141-157
ISSN: 1432-2013
0031-6768
Popis: 1. In frog atria, time and voltage dependence of inactivation and reactivation of fast transient Na current were studied using the sucrose-gap voltage clamp technique. Experiments were done at 4–7° C. 2. Fast inward current inactivated by conditioning depolarizing clamps. The relation between steady-state inactivation and membrane potential is represented by an S-shaped curve similar to that observed in squid axon. At the resting level the availability of the Na-carrying system is about 60–70%. 3. During depolarizing clamps inactivation of Na current follows an approximately exponential time course with time constants between 1.5 and 8 msec. 4. Recovery from inactivation (reactivation) is much slower than development of inactivation. Time constants between 100 and 600 msec were observed during the recovery process following a repolarization or a hyperpolarization. 5. A ratio between the time constants of inactivation and reactivation in the order of 1∶50 was found when the two processes were studied at the same potential level. 6. In the frog atrial action potential the slow reactivation of the Na system is reflected by a relative refractory period reaching far beyond full repolarization. 7. Assuming that the slow course of Na reactivation is an inherent feature of Na kinetics, the inactivation variable (h) of the Hodgkin-Huxley theory (1952d) seems inadequate to describe the inactivation-reactivation process in frog atria. Formally fast inactivation and slow reactivation could be accounted for by replacing the variableh with two variables which both decrease on depolarization but largely differ in the rate constants.
Databáze: OpenAIRE
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