Fendiline-induced Ca ²⁺ movement in A10 smooth muscle cells

The effect of fendiline, an anti-anginal drug, on cytosolic free Ca ²⁺ levels ([Ca ²⁺ ] _i ) in A10 smooth muscle cells was explored by using fura-2 as a Ca ²⁺ indicator. Fendiline at concentrations between 10-50 μM increased [Ca ²⁺ ] _i in a concentration-dependent manner with an EC50 of 20 μM. External Ca ²⁺ removal reduced the Ca ²⁺ signal by 75%. Addition of 3 mM Ca ²⁺ increased [Ca ²⁺ ] _i in cells pretreated with fendiline in Ca ²⁺ -free medium. The 50 μM fendiline-induced [Ca ²⁺ ] _i increase in Ca ²⁺ -containing medium was inhibited by 10 μM of La ³⁺ , nifedipine, or verapamil. In Ca ²⁺ -free medium, pretreatment with 1 μM thapsigargin (an endoplasmic reticulum Ca ²⁺ pump inhibitor) to deplete the endoplasmic reticulum Ca ²⁺ store partly inhibited 50 μM fendiline-induced Ca ²⁺ release; whereas pretreatment with 50 μM fendiline abolished 1 μM thapsigargin-induced Ca ²⁺ release. Inhibition of phospholipase C activity with 2 μM U73122 did not alter 50 μM fendiline-induced Ca ²⁺ release. Incubation with 50 μM fendiline for 10-30 min decreased cell viability by 10-20%. Together, the findings indicate that in smooth muscle cells fendiline induced [Ca ²⁺ ] _i increases. Fendiline acted by activating Ca ²⁺ influx via L-type Ca ²⁺ channels, and by releasing internal Ca ²⁺ in a phospholipase C-independent manner. Prolonged exposure of cells to fendiline induced cell death.