DEVELOPMENTAL-CHANGE IN THE VOLTAGE-DEPENDENCE OF THE PACEMAKER CURRENT, I(F), IN RAT VENTRICLE CELLS

Myocytes were isolated from newborn and adult rat ventricle. Using the whole-cell patch clamp, the two cell. populations were compared for t he presence of the hyperpolarization-activated pacemaker current i(f). As in other mammalian species, the threshold voltage in acutely disso ciated adult rat myocytes was extremely negative (-113 +/- 5 mV; n=12) . In contrast, threshold in newborn cells was relatively positive, reg ardless of whether measured in acutely dissociated (-72 +/- 2 mV; n=6) or cultured cells (-70 +/- 2 mV; n=9). Current density was not reduce d in the adult. These results suggest that with development the ventri cle assumes its non-pacemaker function, at least in part, by a shift o f the voltage dependence of i(f) outside the physiological range.