Calcium-movement controlling cardiac contractility II. Analog computation of cardiac excitation-contraction coupling on the basis of calcium kinetics in a multi-compartment model.

Abstract A computer model for excitation-contraction coupling in mammalian cardiac cells was designed based on calcium movements in a multicompartment system. The model includes an extracellular space of constant calcium concentration from which calcium crosses the membrane and reaches the myoplasma by a voltage and time dependent process. The free myoplasmic calcium content is considered to reflect the intensity of the active state. Calcium can be taken up either by a carrier-sustained two step reaction into a compartment representing some parts of the longitudinal system or into another pool representing mitochondria. Calcium can leave the cell or can be released again into the myoplasma by a second order reaction. The behaviour of the model is compared to that of living cardiac ventricular muscle. The model correctly predicts the following groups of inotropic phenomena. Steady state and dynamic force-frequency relationships, positive and negative staircases after both changes of frequency and AP-duration, mechanical transients after a period of rest and aftercontractions.