Cadmium‐induced Cytosolic Ca2+ Elevation and Subsequent Apoptosis in Renal Tubular Cells

Abstract: 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 µM. 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 µM thapsigargin (an endoplasmic reticulum Ca2+pump inhibitor) and 2 µM 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 µM, Cd2+killed cells in a concentration‐dependent manner. The cytotoxic effect of 100 µM 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.