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 ([Ca2+](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 microM. Cd2+-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 microM thapsigargin (an endoplasmic reticulum Ca2+pump inhibitor) and 2 microM 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 microM, Cd2+killed cells in a concentration-dependent manner. The cytotoxic effect of 100 microM 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.