Effect of nortriptyline on intracellular Ca ²⁺ handling and viability in canine renal tubular cells

In Madin-Darby canine kidney (MDCK) cells, the effect of nortriptyline, an antidepressant, on intracellular Ca ²⁺ concentration ([Ca ²⁺ ] _i ) was measured by using fura-2. Nortriptyline (>10 μM) caused a rapid increase of [Ca ²⁺ ] _i in a concentration-dependent manner (EC ₅₀ = 75 μM). Nortriptyline-induced [Ca ²⁺ ] _i increase was prevented by 40% by removal of extracellular Ca ²⁺ but was not altered by voltagegated Ca ²⁺ channel blockers. In Ca ²⁺ -free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca ²⁺ -ATPase, caused a monophasic [Ca ²⁺ ] _i increase, after which the increasing effect of nortriptyline on [Ca ²⁺ ] _i was abolished; also, pretreatment with nortriptyline reduced a large portion of thapsigargin-induced [Ca ²⁺ ] _i increase. U73122, an inhibitor of phospholipase C, abolished ATP (but not nortriptyline)-induced [Ca ²⁺ ] _i increase. Overnight incubation with 10 μM nortriptyline decreased cell viability by 16%, and 50 μM nortriptyline killed all cells. Prechelation of cytosolic Ca ²⁺ with BAPTA did not alter nortriptyline-induced cell death. These findings suggest that nortriptyline rapidly increased [Ca ²⁺ ] _i in renal tubular cells by stimulating both extracellular Ca ²⁺ influx and intracellular Ca ²⁺ release, and was cytotoxic at higher concentrations in a Ca ²⁺ -dissociated manner.