Combined Effects of Calcium and Potassium on Contractility and Excitability of the Mammalian Myocardium

Abstract

The effect of K on excitability and contractility of the isolated papillary muscle of the cat was studied in Krebs-Henseleit soln. at 3 levels of Ca: 1.5, 2.0, and 2.5 mM/l. At all levels of Ca, concns. of K between 2.15 and 10.15 mM/1. had no effect on contractility; beyond 10.15 mM/1., K diminished contractile force. K increased excitability of the muscle between 2.15 and 8.15 mM/1.; between 8.15 and 11.15 mM K/l., excita-bility remained constant, and beyond 11.15 mM K/l., excitability diminished. Whether the muscle was treated for 5 min. or 1 hr., results were similar. Ca increased contractility and diminished excitability. Varying Na concns. from 130-160 mM/l. influenced neither contractility nor excitability. An analysis of variance showed a lack of interaction between Ca and K, thus failing to substantiate any proposed Ca-K ratio. Each ion appears to exert an independent action. These observations show that excitability and contractility are separable phenomena.