CYTOCHROME-P450 - A NOVEL SYSTEM MODULATING CA2-CELLS( CHANNELS AND CONTRACTION IN MAMMALIAN HEART)

1. Cytochrome P450 (P450) is a ubiquitous enzyme system that catalyses oxidative reactions of numerous endogenous and exogenous compounds. T he modulatory effects of P450 on the L-type Ca2+ current (I-Ca), intra cellular free Ca2+ signals and cell shortening were assessed in adult rat single ventricular myocytes.2. Bath administration of the imidazol e antimycotics, clotrimazole, econazole and miconazole, which are pote nt P450 inhibitors, significantly suppressed cardiac I-Ca. While the C a2+ channel antagonist nifedipine blocked I-Ca within 30 s, clotrimazo le-induced suppression of I-Ca required 5.1 +/- 0.4 min (n = 14) to re ach a steady low level. The suppression of I-Ca was dose dependent and recovered after washout of clotrimazole. Intracellular dialysis with the P450 antibody anti-rat CYP1A2 also significantly reduced cardiac I -Ca. 3. Additional administration of the beta-adrenergic agonist isopr enaline (1 mu M) or the membrane-permeable 8-bromo-cAMP (2 mite) compl etely reversed the suppressant effects of clotrimazole and NaCN on I-C a. In addition, intracellular dialysis with 2 mite GAMP abolished the P450 inhibitor-induced suppression of I-Ca. Phosphorylation of the cha nnel with hydrolysis-resistant ATP gamma S prevented the suppressant e ffect of clotrimazole on I-Ca. Furthermore, dephosphorylation of the C a2+ channel with intracellular dialysis with phosphatase types I and I I reduced I-Ca by 85 +/- 3% and abolished clotrimazole-induced suppres sion of I-Ca. 4. Extracellular administration of the phospholipase A(2 ) inhibitors mepacrine and 4-bromophenacyl bromide significantly suppr essed I-Ca. 5. Clotrimazole, econazole, miconazole and CN- also signif icantly inhibited intracellular free Ca2+ signals and cell shortening in rat single ventricular myocytes. 6. Intracellular cAMP content was significantly reduced in isolated ventricular myocytes incubated with clotrimazole or CN-. Extracellular administration of 11,12-epoxyeicosa trienoic acid, one of the P450-mediated metabolites of arachidonic aci d, enhanced I-Ca and intracellular cAMP content. The epoxyeicosatrieno ic acid also restored the amplitude of the reduced I-Ca in P450 antibo dy-dialysed myocytes. 7. The present data suggest that cytochrome P450 modulates cardiac I-Ca and cell contraction, and the modulation may r esult from changes in intracellular levels of cAMP by P450-mediated me tabolites of arachidonic acid.