Cadmium-induced cytosolic Ca²⁺ elevation and subsequent apoptosis in renal tubular cells

Cadmium (Cd²⁺) is an industrial and environmental metal. The effect of Cd²⁺ on intracellular free-Ca²⁺ levels ([Ca ²⁺]_i) and viability in Madin Darby canine kidney cells was explored. Cd²⁺increased [Ca²⁺]_i in a concentration-dependent manner with an EC₅₀ of 85 ̄M. Cd ²⁺-induced Mn²⁺ entry demonstrated Ca²⁺ influx. Removal of extracellular Ca²⁺ decreased the [Ca²⁺] _i signal by 60%. The [Ca²⁺]_i signal was inhibited by La³⁺ but not by L-type Ca²⁺ channel blockers. In Ca²⁺-free medium, Cd²⁺-induced [Ca²⁺] _i signal was abolished by pre-treatment with 1 ̄M thapsigargin (an endoplasmic reticulum Ca²⁺pump inhibitor) and 2 ̄M carbonylcyanide m-chlorophenylhydrazone (CCCP; a mitochondrial uncoupler). Cd²⁺-induced Ca²⁺ release was not altered by inhibition of phospholipase C. At concentrations between 10 and 100 ̄M, Cd ²⁺killed cells in a concentration-dependent manner. The cytotoxic effect of 100 ̄M Cd²⁺was reversed by pre-chelating cytosolic Ca²⁺with BAPTA. Cd²⁺-induced apoptosis was demonstrated by propidium iodide. Collectively, this study shows that Cd²⁺ induced a [Ca²⁺]_i increase in Madin Darby canine kidney cells via evoking Ca²⁺ entry through non-selective Ca²⁺ channels, and releasing stored Ca²⁺ from endoplasmic reticulum and mitochondria in a phospholipase C-independent manner.