title: Biphasic time course of inactivation of potassium contractures in single twitch muscle fibers of the frog.
abstract: The time course of the inhibition of peak tension (inactivation) of potassium contracture induced by conditioning depolarization with 10, 15, 20 and 30 mM K+ was examined, using single twitch fibers from the frog semitendinosus muscle. The time-dependence curve of the inactivation was biphasic, consisting of the first phase and the second phase. The first phase was characterized as follows: 1) the time course and the extent depend on the degree of conditioning depolarization; 2) the inactivation proceeds exponentially and finally reaches a steady level; and 3) the rate is markedly increased by lowering Ca2+ in the external medium. It could be considered that the first phase of the inactivation is an analogical phenomenon with the inactivation of sodium conductance in a squid giant axon. The second phase of the inactivation induced by conditioning with 20 and 30 mM K+ reached its full inactivation independently of the degree of conditioning depolarization. On the basis of these results, the terms inactivation 1 and inactivation 2 were given to the first phase and second phase, respectively, of the time-dependence curve of the inactivation of potassium contracture.
mesh_terms: D000818:Animals; D001001:Anura; D002118:Calcium / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D011898:Ranidae; D013997:Time Factors
chemical_list: D011188:Potassium; D002118:Calcium