Action potentials of guinea pig atria under conditions which alter contraction

¹ Department of Physiology, Washington University School of Medicine, St. Louis, Missouri, and Department of Pharmacology, State University of New York, Down State Medical Center, Brooklyn, New York

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.

Key Words: inotropic agents • ryanodine • strophanthin • calcium transmembrane action potentials • contractile strength of cardiac muscle • spontaneous experimental heart failure • rest intervals and "postrest" beats

Submitted on January 28, 1963