Kinetic Aspects of Calcium Current in Ventricular Myocardial Fibres

Abstract

The application of the voltage clamp technique to cardiac Purkinje fibres (Deck, Kern & Trautwein, 1964) suggests that, in the region of the plateau of the action potential, there are permeability changes which are dependent on voltage and time and which involve most of the ions in the extracellular fluid (Noble & Tsien, 1969). Thus, beside sodium ions, calcium ions contribute to the total depolarizing membrane current during rather strong depolarization (Reuter, 1967). Recent experiments by Niedergerke & Orkand (1966) and by Rougier, Vassort, Gamier, Gargouil & Coraboeuf (1968) have shown that calcium ions may also contribute a charge during the action potential plateau of frog myocardium. In addition to the significance for the action potential, the flow of calcium ions across the membrane might be important for activation of the contractile proteins. Therefore it seemed worthwhile to investigate the kinetics of calcium current in cardiac preparations in greater detail.