Summary
The cardiac slow inward current (Isi) is mediated by a specific conductance system, the slow channel. It is highly selective for Ca and other bivalent cations as for instance Sr, whilst Na permeability is extremely small. The kinetics of activation, inactivation and recovery from inactivation are voltage-and temperaturesensitive. In contrasts to the Hodgkin-Huxley model, development and removal of inactivation operate with different time constants, at least in the ventricular myocardium of cats. Moreover, both processes exhibit a different pharmacological susceptibility. Thus a second inactivation variable having smaller rate constants than the inactivation variable f has to be introduced, which simultaneously suggests the existence of slow inactivation in cardiac slow channels.
Zusammenfassung
Der langsame Einwärtsstrom (Isi) der Herzmuskelzelle wird durch ein spezifisches Leitfähigkeitssystem vermittelt. Dieser langsame Membrankanal besitzt eine hohe Selektivität für Ca++ und andere bivalente Kationen wie beispielsweise Sr++. Seine Na+-Permeabilität ist dagegen nur gering. Aktivation, Inaktivation und „recovery from inactivation” sind potential- und temperaturabhängige Prozesse. Wenigstens am Ventrikelmyokard der Katze sind im Gegensatz zum Hodgkin-Huxley-Modell Entwicklungs- und Abklingkinetik der Inaktivation nicht identisch. Beide Prozesse weisen eine differente Empfindlichkeit gegenüber Verapamil auf. Diese Besonderheiten zwingen zur Einführung einer zweiten Inaktivationsvariablen, deren Zeitkonstanten größer als die der Inaktivationsvariablen f sind, was gleichbedeutend mit der Annahme eines langsamen Inaktivationsprozesses ist.
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Kohlhardt, M. Slow channel kinetics in heart muscle. Basic Res Cardiol 76, 589–601 (1981). https://doi.org/10.1007/BF01908049
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DOI: https://doi.org/10.1007/BF01908049