Low-threshold current is major calcium current in chick ventricle cells

Single myocytes were dissociated from the apical ventricles of 14-day-old chick embryos and were maintained in culture for 24 h. Isolated rounded cells, 13-18 microns in diameter with input capacitance averaging 5.2 pF, were selected for whole cell patch-clamp analysis of calcium current (ICa). Two current components, T-type (IT) and L-type (IL), were identified by differences in their voltage thresholds and pharmacological sensitivity, IL was activated by depolarizing steps from -40 mV and was selectively blocked by 1 microM D 600 (methoxyverapamil). IT was obtained by subtracting IL from total ICa and was blocked by 120 microM Ni2+. Identified by threshold potential, sensitivity to Ni2+, or resistance to D 600, IT had a greater current density than has been reported in any adult cardiac tissue. It was also larger than IL and was therefore the major contributor to ICa in this preparation.