INHIBITION OF CYTOCHROME-P-450 REDUCES VOLTAGE-GATED K+ CURRENTS IN PULMONARY ARTERIAL MYOCYTES

Cytochrome P-450 (P-450) is a NADPH-requiring and O-2-dependent monooxygenase system. It is present in lung and has been postulated to act as an O-2 sensor in hypoxic pulmonary vasoconstriction. To determine whether P-450 is involved in the regulation of voltage-gated K+ (K-V) channel activity in pulmonary artery (PA) myocytes, we used the whole cell patch-clamp technique to evaluate the effects of P-450 inhibitors on K-V channel currents (I-KV) and membrane potential (E(m)). Bath application of the P-450 inhibitors clotrimazole, miconazole, and 1-aminobenzotriazole (1-ABT) significantly and reversibly inhibited steady-state I-KV (I-Kss) and depolarized PA cells bathed in either Ca2+-containing (1.8 mM) or Ca2+-free [0.5-1 mM ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid present] bath solution. Clotrimazole (1 mu M), miconazole (10 mu M), and 1-ABT (1 mM) reversibly I-Kss elicited by a test potential of +80 mV, by 40, 70, and 31%, respectively. Pretreatment of PA smooth muscle cells with 10 mM 4-aminopyridine (4-AP) prevented the subsequent inhibitory effect of clotrimazole on I-KV. However, pretreatment of the cells with 1 mM tetraethylammonium negligibly altered the effects of miconazole on I-KV and E(m). In current-clamp (I = 0) measurements, clotrimazole depolarized PA myocytes by 9 and 11 mV during perfusion with Ca2+ containing and Ca2+-free bath solution, respectively. 1-ABT also caused a 9-mV depolarization in PA myocytes bathed in Ca2+-free solution. These effects are similar to those induced by hypoxia, reduced glutathione, and 4-AP. Clotrimazole also decreased I-KV and depolarized mesenteric arterial myocytes. These data raise the possibility that the P-450 system, due to its influence on I-KV and sensitivity to O-2 tension and NADPH, may play a role in linking the regulation of pulmonary vascular tone to the alteration of cellular redox status through a common pathway of Ky channel activity.