Developmental changes in time course of recovery from inactivation in L-type calcium currents of rabbit ventricular myocytes

The mechanisms of recovery from inactivation of the L-type calcium current (I(Ca)) are not well established, and recovery is affected by many experimental conditions. Little is known about developmental changes of recovery from inactivation of I(Ca). We studied developmental changes of recovery from inactivation in I(Ca) using isolated adult and newborn (1-4 days) rabbit ventricular myocytes. We used broken-patch and perforated-patch techniques with physiological extracellular ionic concentrations of calcium and sodium and interpulse conditioning potentials of -80 or -50 mV. We also maximized I(Ca) with forskolin. We found that recovery from inactivation did not differ between adult and newborn cells when either EGTA or BAPTA was used to buffer intracellular calcium. Maximizing I(Ca) with forskolin slowed recovery from inactivation in newborn but not in adult cells. In contrast, when the intracellular buffering of the cell was left nearly intact (perforated patch), recovery from inactivation (half-time of recovery) in the newborn cells was significantly slower than for the adult cells when either a conditioning potential of -80 mV (140 +/- 9 vs. 58 +/- 4 ms, newborn vs. adult; P < 0.05) or -50 mV (641 +/- 106 vs. 168 +/- 15 ms, newborn vs. adult; P < 0.05) was used. Forskolin significantly increased half-time of recovery for both adult and newborn cells. Dialysis with no calcium buffer showed a slower recovery from inactivation in newborn cells. Intracellular dialysis with a calcium buffer masked differences in recovery from inactivation of I(Ca) between newborn and adult rabbit ventricular cells.