Inhibition of voltage‐gated Ca ²⁺ entry into GH ₃ and chromaffin cells by imidazole antimycotics and other cytochrome P450 blockers

Abstract

We have studied the effects of cytochrome P450 inhibitors on the entry of Ca2+ and Mn2+, used here as a Ca2+ surrogate for Ca2+ channels, in fura-2-loaded GH3 pituitary cells and bovine chromaffin cells depolarized with high-K+ solutions. Imidazole antimycotics were potent inhibitors (econazole greater than miconazole greater than clotrimazole greater than ketoconazole). alpha-Naphtoflavone and isosafrole, but not metyrapone, also inhibited the entry of Ca2+ and Mn2+ induced by depolarization. This inhibitory profile most resembles that reported for IA-type cytochrome P450. However, carbon monoxide (CO), a well-known cytochrome P450 antagonist, had no effect on Ca2+ (Mn2+) entry. Given the high selectivity of the imidazole antimycotics for the heme moiety, our results suggest that a hemoprotein closely related to cytochrome P450 (but insensitive to CO) might be involved in the regulation of voltage-gated Ca2+ channels. The inhibitory pattern was also similar to that previously reported for agonist-induced Ca2+ (Mn2+) influx in neutrophils and platelets, although CO was an efficient inhibitor in this case. These results pose the question of whether similarities in the sensitivity to cytochrome P450 inhibitors exhibited by receptor-operated and voltage-gated channels reflect unknown similarities either in structural features or regulation mechanisms.

Therapy with oral clotrimazole induces inhibition of the Gardos channel and reduction of erythrocyte dehydration in patients with sickle cell disease.

“…These effect include inhibition of Ca 2ϩ entry via the dihydropyridine-sensitive Ca 2ϩ channels of the plasma membrane (35,36), inhibition of cell proliferation (37), and blockade of release of von Willebrand factor from cultured endothelial cells (38,39). Studies in a mouse model for ␤ thalassemia have indicated that combination of CLT with either recombinant human erythropoietin (r-HuEPO) or hydroxyurea induces a greater increase in Hb levels compared to therapy with r-HuEPO or hydroxyurea alone (40).…”

Effects of cytochrome P450 inhibitors on EDHF‐mediated relaxation in the rat hepatic artery

“…Thus, when such channels are closed by nimodipine in the rat hepatic artery, the subsequent relaxations to EDHF and levcromakalim are reduced (Zygmunt 1994b). Since cytochrome P450 inhibitors, including clotrimazole and proadifen, are also inhibitors of voltage-sensitive Ca-channels (Kalsner et al, 1970;Triggle et al, 1979;Villalobos et al, 1992), this action may thus contribute to their effect on EDHF-mediated relaxations. Fulton et al (1994) showed that clotrimazole had no effect on the vasodilatation produced by bolus injections of cromakalim into rat coronary arteries.…”

Two different constituents of plasma increase cytosolic calcium selectively in neurons or glia of primary rat cerebellar cultures.

“…[Ca2+], measurements were performed as described previously (Villalobos, Fonteriz, Lopez, Garcia & Garcia-Sancho, 1992;Lopez, Garcia, Artalejo, Neher & Garcia-Sancho, 1995). Briefly, cell-coated coverslips loaded with fura-2 AM (the acetoxymethyl ester form of fura-2; Grynkiewicz, Poenie & Tsien, 1985) were placed under the inverted microscope (Nikon Diaphot, x40 oilimmersion objective lens) and fluorescence images were processed using an Applied Imaging MagiCal image processor (Sunderland, UK).…”