Depression of the Spontaneous Activity by Phorbol Esters in Young Embryonic Chick Cardiomyocytes

[摘要] References(43)Cited-By(6)Effects of phorbol esters, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and 4-β-phorbol-12, 13-dibutyrate (PDB), that stimulate protein kinase C (PK-C) on the spontaneous action potential and the ionic currents in cultured embryonic chick ventricular cardiomyocytes were examined using whole-cell voltage-clamp and current-clamp modes. Experiments were performed at room temperature (22°C). The firing rate of spontaneous activity was 61.7± 1.6 beats/min (n=12). Phorbol esters (100 nM and 1 μM) caused a negative chronotropic effect, and they inhibited the maximum rate of depolarization and the action potential amplitude. The action potential duration (at 50% repolarization) tended to decrease, and the maximum diastolic potential was unaffected. In whole-cell voltage-clamp experiments, both TPA and PDB inhibited the L-type Ca2+ current and the delayed rectifier K+ current. The fast time constant of the inactivation phase for the Ca2+2+ current was decreased, but the slow component was unaffected. In addition, PDB (100 nM) enhanced the T-type Ca2+ current, accompanied with an increase in its time constant. In contrast, 4-&aipha;-phorbol-12, 13-didecanoate (PDD), an inactive analogue on PK-C, failed to produce significant changes. These results suggest that the PK-C stimulation induced by phorbol esters might affect the ionic currents and modulate the [Ca]i, resulting in regulation of the spontaneous activity of embryonic chick heart cells.

[学科分类] 药理学

[关键词] Phorbol ester;Protein kinase C;Automaticity;Ionic current;Embryonic chick heart cell