Frog muscle fibre action potential and different extracellular calcium concentration at lowered pH in the medium.

Abstract

This article is mainly concerned with the influence of Ca2+[o in acidified extracellular medium on the intracellular action potentials (ICAPs) and total ionic current (Ii) during ICAP of isolated skeletal muscle fibre. The bundles of frog muscle fibres were bathed in Ringer's solution with standard Ca2+[o at pH 6.5 after which the fibres were exposed for 30 min to Ca(2+)-free solution and Ca(2+)-enriched solution at pH 6.5. The ICAPs in standard Ca2+[o solution (control) and after exposure for 30 min to Ringer's solutions with different Ca2+[o at pH 6.5 were recorded and the Ii during ICAP was calculated. The ICAP amplitude from the fibres in Ca(2+)-free solutions at pH 6.5 showed a significant increase vs. control, while the time characteristics if the ICAPs in different Ca2+[o decreased except for the ICAP depolarization phase duration in Ca(2+)-enriched solution. The Ii alterations reflect ICAP changes. It was suggested that the changed Ca2+[o at pH 6.5 compensated to some extent the observed inhibitory effect of lowered pH on ICAP parameters in solution with standard Ca2+[o.