Different Densities of Na-Ca Exchange Current in T-Tubular and Surface Membranes and Their Impact on Cellular Activity in a Model of Rat Ventricular Cardiomyocyte

Abstract

The ratio of densities of Na-Ca exchanger current ( NaCa ) in the t-tubular and surface membranes ( NaCa -ratio) computed from the values of NaCa and membrane capacitances ( m ) measured in adult rat ventricular cardiomyocytes before and after detubulation ranges between 1.7 and 25 (potentially even 40). Variations of action potential waveform and of calcium turnover within this span of the NaCa -ratio were simulated employing previously developed model of rat ventricular cell incorporating separate description of ion transport systems in the t-tubular and surface membranes. The increase of NaCa -ratio from 1.7 to 25 caused a prolongation of APD (duration of action potential at 90% repolarisation) by 12, 9, and 6% and an increase of peak intracellular Ca 2+ transient by 45, 2+ transient was a consequence of a higher Ca 2+ load in sarcoplasmic reticulum induced by the increased Ca 2+ cycling between the surface and t-tubular membranes. However, the reason for large differences in the NaCa -ratio assessed from measurements in adult rat cardiomyocytes remains to be explained