Effect of the antidepressant maprotiline on calcium movement and the viability of renal tubular cells

In Madin-Darby canine kidney (MDCK) cells, the effect of maprotiline, an antidepressant, on intracellular Ca²⁺ concentration ([Ca ²⁺]_i) was measured using fura-2. Maprotiline (> 2.5 μM) caused a rapid rise of [Ca²⁺]_i in a concentration-dependent manner (EC₅₀ 200 μM). Maprotiline-induced [Ca²⁺]_i rise was reduced by removal of extracellular Ca²⁺ or by addition of La³⁺, but was not altered by voltage-gated Ca²⁺-channel blockers. Maprotiline-induced Mn ²⁺ influx-associated fura-2 fluorescence quench directly suggests that maprotiline caused Ca²⁺ influx. In Ca²⁺-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca²⁺-ATPase, caused a monophasic [Ca²⁺]_i rise, after which the increasing effect of maprotiline on [Ca²⁺]_i was nearly abolished; also, pretreatment with maprotiline reduced a portion of thapsigargin-induced [Ca²⁺]_i rise. U73122, an inhibitor of phospholipase C, abolished [Ca²⁺]_i rise induced by ATP (but not by maprotiline). Overnight incubation with 1-10 μM maprotiline enhanced cell viability, but 20-50 μM maprotiline decreased it. These findings suggest that maprotiline rapidly increases [Ca²⁺] _i in renal tubular cells by stimulating both extracellular Ca ²⁺ influx and intracellular Ca²⁺ release, and may modulate cell proliferation in a concentration-dependent manner.