Ca2+ channel modulation alters halothane-induced depression of ventricular myocytes.

PURPOSE This study examined the direct myocardial depressant effect of halothane and determined whether an L-type Ca2+ channel agonist and antagonists altered the myocardial depression induced by halothane in cultured rat ventricular myocytes. METHODS Ventricular myocytes were obtained from neonatal rats by enzymatic digestion with collagenase and then cultured for 6 to 7 days. The myocytes were stabilized in a serum-free medium, and the spontaneous beating rate and amplitude were measured. To assess the halothane-induced conformational changes in L-type Ca2+ channel, receptor binding study was performed using a dihydropyridine derivative, [3H] PN 200-110, in cardiac membrane preparation. RESULTS Halothane (1%, 2%, 3%, 4%) decreased the beating rate and amplitude in a concentration-dependent manner (P < 0.05). The myocardial depressant effects of halothane were potentiated by nifedipine or verapamil (P < 0.05). Bay K 8644, an L-type Ca2+ channel agonist, completely prevented the halothane-induced depression in amplitude (P < 0.05), but affected the beating rate less. Adding halothane (2%) decreased (P < 0.05) the maximum binding site density for [3H] PN 200-110 (from 198.6 +/- 23.7 fmol.mg-1 protein to 115.3 +/- 21.6 fmol.mg-1 protein) but did not affect binding affinity (from 0.461 +/- 0.077 nM to 0.307 +/- 0.055 nM). CONCLUSION The reduction of Ca2+ current via sarcolemmal L-type Ca2+ channel, probably due to conformational changes in dihydropyridine binding sites, plays an important role in halothane-induced myocardial depression in living heart cells.