CALPAINS MEDIATE CALCIUM AND CHLORIDE INFLUX DURING THE LATE-PHASE OFCELL INJURY

The role of Ca++ in cell death is controversial, Extracellular Ca++ in flux and calpain activation occurred during the late phase of renal pr oximal tubule cell injury produced by'ihe mitochondrial inhibitor anti mycin A. Chelation of intracellular Ca++, extracellular Ca++, the calc ium channel blocker nifedipine, calpain inhibitor 1 and the dissimilar calpain inhibitor PD150606 blocked antimycin A-induced influx of extr acellular Ca++ and cell death, The calcium channel blocker verapamil w as ineffective. Calpain inhibitor 1 and PD150606 were cytoprotective a lso against tetrafluoroethyl-L-cysteine-, bromohydroquinone-, oxidant (t-butylhydroperoxide)- and calcium ionophore (ionomycin)-induced cell death, Extracellular Ca++ influx was associated with the translocatio n of calpain activity from the cytosol to the membrane and was prevent ed by calpain inhibitor 1, PD150606 and nifedipine, Finally, nifedipin e, calpain inhibitor 1, PD150606 and the Cl- channel inhibitors [5-nit ro-2-(3-phenylpropylamino)-benzoate, niflumic acid, diphenylamine-2-ca rboxylate, and indanyloxyacetic acid] blocked the increase in Cl- infl ux that occurs during the late phase of cell injury and triggers termi nal cell swelling and death, These data suggest that Ca++ and calpains play a common and critical role in renal proximal tubule cell death p roduced by diverse agents, In addition, calpain activation appears to play a dual role during the late phase of cell injury, Initial calpain activation elicits extracellular Ca++ influx through a nifedipine-sen sitive pathway, resulting in calpain translocation to the membrane and in turn Cl- influx.