Long openings of calcium channels in fetal rat ventricular cardiomyocytes

Whole-cell and single-channel Ca²⁺ currents (I_Ca) of single fetal (12 – 18 days) and neonatal (1 – 10 d) rat ventricular myocytes were recorded using patch clamp techniques. Whole-cell I_Ca density increased markedly during the fetal period and remained almost constant during the neonatal period. In cell-attached patch recordings (with 110 mM Ba²⁺ in the pipette), the L-type Ca²⁺ channels, observed on both fetal d-12 and neonatal d 5, had the same conductance (23 pS). On fetal d-12, many relatively long openings were observed in addition to brief openings, whereas on neonatal d-5, long openings were less observed and brief openings dominated. Therefore, long openings of the Ca²⁺ channels occur in early development in rat heart cells, similar to that reported for chick hearts [7, 8]. The increase of the whole-cell current amplitude observed during development may be due to an increase in available channel number.