Clotrimazole inhibits the recombinant human cardiac L‐type Ca 2+ channel α 1C subunit

Clotrimazole (CLT) is an antimycotic agent with a potential role in the treatment of cancer. Whole‐cell patch clamp recordings and Fura‐2 AM fluorescence measurements were used to investigate the inhibition by CLT of recombinant human cardiac L‐type Ca 2+ channel α 1C subunits, stably expressed in human embryonic kidney (HEK 293) cells. CLT (100 nmol l −1 to 25 μmol l −1 ) reduced Ca 2+ channel currents in a concentration‐dependent manner. Inhibition was neither use‐ or voltage‐dependent. The effects of CLT were rapid and maximal effects were attained within 3 min. Application of CLT also caused an acceleration of apparent Ca 2+ channel current inactivation. Basal current density and the degree of inhibition due to CLT were not significantly altered by pretreating cells with 3 mmol l −1 1‐aminobenzotriazole for 1 h, or by dialysing cells for 10 min with 2 mmol l −1 α‐napthoflavone via the patch pipette, suggesting that the inhibitory action of CLT was not due to inhibition of cytochrome P ‐450. CLT (10 μmol l −1 ) did not influence [Ca 2+ ] i , as determined by Fura‐2 AM fluorescence measurements. Dialysing cells for 10 min with the non‐specific serine/threonine kinase inhibitor H‐7 (10 μmol l −1 ) was without effect on basal current density or on the inhibitory response to 10 μmol l −1 CLT, indicating that CLT is not acting via an indirect effect on these kinases. These data suggest that CLT exerts a direct blocking effect on the α 1C subunit at therapeutic concentrations. This effect may explain the abbreviation of the action potential duration by CLT observed in cardiac myocytes.British Journal of Pharmacology (2000) 129 , 547–554; doi: 10.1038/sj.bjp.0703106