| The early events during oncosis (necrotic cell death) include inhibition of cellular respiration, loss of intracellular ATP, K+ efflux and Na+ influx. The role of intracellular Ca 2+ stores during these events has not been completely elucidated. The aims of these studies were to examine the events that occur during the early phase of oncotic cell death in rabbit renal proximal tubules (RPT) and the efficacy of numerous calpain inhibitors in the prevention of oncotic cell death. Experiments were designed to examine the role of the endoplasmic reticulum (ER) Ca2+ store, increases in cytosolic free Ca2+ (Ca2+f) levels, and calpain activity following mitochondrial inhibition and yielded the following results: Antimycin A produced a rapid depletion of ATP, followed by the release and depletion of the ER Ca 2+ store. Correlating with ER Ca2+ release was an increase in Ca2+f levels and a corresponding increase in calpain activity. Cell death, measured by the release of lactate dehydrogenase, occurred 30 min after antimycin A addition. Prior depletion of ER Ca 2+ stores prevented or reduced antimycin A- and tetrafluoroethyl-l-cysteine (TFEC)-induced cell death/lysis. Chelation of extracellular Ca2+, as well as treatment with various calpain inhibitors (calpain inhibitor 1, GT1, SJA 7019, and SJA 7029), also prevented antimycin A-induced cell death/lysis. Calpain inhibition prevented the late-stage uptake of Ca2+, even when the inhibitors were added 10 min after antimycin A. These studies suggest that during the early phase of RPT cell injury, ATP depletion triggers the release of ER Ca2+ and a corresponding increase in Ca 2+f levels, resulting in increased calpain activity. The increased calpain activity mediates the late stages of cell death, including influx of extracellular Ca2+, Cl−, and H2O, terminal cell swelling and death/lysis. |
