Is potassium conductance of cardiac Purkinje fibres controlled by [Ca²⁺]_i?

Abstract

ELEVATED extracellular Ca²⁺ concentration¹, prolonged treatment with high doses of cardiac glycosides², and metabolic inhibition³ shorten the action potential of cardiac muscle. In these conditions the intracellular free Ca²⁺ may be increased and an increase in intracellular Ca²⁺ could produce shortening of the action potential either by affecting the Ca²⁺ inward current or by increasing the potassium permeability⁴. The latter mechanism has been observed in red blood cells⁵ and in the neurones of some species^6–8. Here I give the results of studying the effect of iontophoretically injected Ca²⁺ in cardiac Purkinje cells. Such injection led to membrane hyperpolarisation and considerable shortening of the action potential, suggesting that the level of intracellular free Ca²⁺ can affect the potassium permeability in cardiac muscle.