Electrical restitution process in dispersed canine cardiac Purkinje and ventricular cells

Rate-dependent changes in cardiac action potential duration (APD) have been related to ion accumulation and depletion in restricted extracellular spaces. Isolated cardiac cells lack intercellular clefts and thus are less likely than intact tissue to experience ionic transients immediately outside the plasma membrane. Furthermore, isolated Purkinje cells lack the T tubules found in ventricular tissue and cells, which also can be a site of ion accumulation and depletion. We therefore employed single canine ventricular and Purkinje cells to investigate the contribution of restricted spaces to the electrical restitution process. In both cell types, abrupt changes in cycle length do not alter resting potential, but APD alters with a time constant of approximately 1 min. In addition, both preparations exhibit two components to the electrical restitution process of the APD. The rapid component has a time constant of 66 +/- 17 ms in the ventricle cells and 186 +/- 43 ms in the Purkinje cells. The slower component is both smaller and more variable. These values are similar to those reported in intact canine ventricular and Purkinje tissue. Thus the restitution process of APD, as measured in these isolated cardiac cells, is not markedly dependent on the presence or absence of restricted extracellular spaces.