Depression of the spontaneous activity by phorbol esters in young embryonic chick cardiomyocytes.
Effects of phorbol esters, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and 4-beta-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 degrees C). The firing rate of spontaneous activity was 61.7 +/- 1.6 beats/min (n = 12). Phorbol esters (100 nM and 1 microM) 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+ 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-alpha-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.
Satoh
H
H
Department of Pharmacology, Nara Medical University, Japan.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002304:Cardiac Pacing, Artificial; D002642:Chick Embryo; D003198:Computer Simulation; D006329:Heart Conduction System / Q000187:drug effects; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects* / Q000196:embryology; D009206:Myocardium / Q000166:cytology* / Q000201:enzymology; D018408:Patch-Clamp Techniques; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D013696:Temperature; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D015220:Calcium Channels; D015221:Potassium Channels; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate