Modelling of intracellular Ca2+ alternans and Ca2+-voltage coupling in cardiac myocytes

In cardiac myocytes, both action potential duration (APD) and mechanical contraction alternans are associated with intracellular Ca²⁺ alternans. The aim of this study is to investigate the interaction between Ca²⁺ and APD alternans by using computer simulations. With a spatially extended (75 elements) model of a single canine ventricular cell, Ca²⁺ and APD alternans were produced either by rapid pacing (3.57 Hz), or by slow pacing (2.5 Hz) with an increased steepness of the relationship between SR Ca²⁺ content and cytoplasimc Ca²⁺ concentration. It is shown that spatially discordant Ca²⁺ alternans is generated when the Ca²⁺-dependent L-type Ca²⁺ channel inactivation is strong. It tends to be concordant for weak Ca²⁺-dependent L-type Ca²⁺ channel inactivation.