Effects of Drugs and Stimulation on 45 Ca Movements in Frog Ventricle

Abstract

Summary

The relation between contractile activity and Ca movements was studied in the frog heart by a method which permitted the continuous determination of cellular ⁴⁵C uptake and of tension. In Ringer solution, stimulation increased ⁴⁵Ca uptake but the extra uptake per beat was too small to explain the initiation of the contraction by itself, indicating the presence of an intracellular Ca store. In Ca-rich solution (30 mM) acetylcholine increased ⁴⁵Ca uptake in quiescent preparations and at the same time induced or increased a contracture. Epinephrine also increased ⁴⁵Ca uptake under these conditions, but caused a rapid drop in tension. These results suggest that both drugs increase the permeability of the membrane for Ca (P _ca); the inhibitory action of epinephrine may be due to increased intracellular storage of Ca.

This work was supported in part by U.S. Public Health Service Grants AM 0257-011 from the National Institute of Arthritis and Metabolic Diseases, and HE 09884 from the National Heart and Lung Institute.