Action potentials of guinea pig atria under conditions which alter contraction

Abstract

Simultaneous recordings were made of action potential ( AP) and contractile strength ( CS) of electrically driven isolated left atria of guinea pigs at 25–27 C under various experimental conditions which alter CS. Reduction of CS produced by decreasing frequency from 1/sec to 0.1/sec, or by spontaneous failure, was associated with only small changes, if any, in AP configuration. The increased CS produced by strophanthin-K or high calcium was associated with shortening of the AP plateau duration; treatment with ryanodine increased AP plateau duration, and decreased CS. The first beat following a 3- to 10-sec rest interval (postrest ( PR) beat) exhibited greater CS, and an AP with shorter plateau and more pronounced "tailing off" than steady-state controls. With high calcium or strophanthin present, PR beats and steady-state beats were nearly identical in both CS and AP. After ryanodine, PR beats were markedly reduced in CS and had prolonged AP plateaus; these changes could be reversed by high calcium or strophanthin. A hypothesis is introduced which accounts for changes in CS under these conditions.