Mechanism of bifonazole-induced [Ca ²⁺ ] _i increases in MDCK renal tubular cells

The effect of the antifungal drug bifonazole on Ca ²⁺ homeostasis in Madin Darby canine kidney (MDCK) cells was investigated. Cell suspensions were loaded with the Ca ²⁺ -sensitive dye fura-2, and the fluorescence changes were measured with a spectrofluorophotometer. At concentrations between 10-80 μM bifonazole increased cytosolic free Ca ²⁺ levels ([Ca ²⁺ ] _i ) in a concentration-dependent manner. The Ca ²⁺ signals were partly inhibited by removing extracellular Ca ²⁺ . Bifonazole (40 μM) released Ca ²⁺ from the store sensitive to 1 μM thapsigargin, an endopolasmic reticulum Ca ²⁺ pump inhibitor. Bifonazole (40 μM) per se induced capacitative Ca ²⁺ entry while reduced 1 μM thapsigargin-induced capacitative Ca ²⁺ entry. Inositol 1,4,5-trisphosphate may be involved in bifonazole-induced Ca ²⁺ release because inhibiting phospholipase C with 2 μM U73122 partly reduced the bifonazole response. Together, bifonazole increased [Ca ²⁺ ] _i in renal tubular cells by inducing intracellular Ca ²⁺ release and extracellular Ca ²⁺ influx.