Endoplasmic reticulum Ca2+ signaling and calpains mediate renal cell death

Abstract

The goal of the current study was to determine the roles of ATP content, endoplasmic reticulum (ER) Ca2+ stores, cytosolic free Ca2+ (Ca2+f) and calpain activity in the signaling of rabbit renal proximal tubular (RPT) cell death (oncosis). Increasing concentrations (0.3-10 μM) of the mitochondrial inhibitor antimycin A produced rapid ATP depletion that correlated to a rapid and sustained increase in Ca2+f, but not phospholipase C activation. The ER Ca2+-ATPase inhibitors thapsigargin (5 μM) or cyclopiazonic acid (100 μM) alone produced similar but transient increases in Ca2+f. Pretreatment with thapsigargin prevented antimycin A-induced increases in Ca2+f and antimycin A pretreatment prevented thapsigargin-induced increases in Ca2+f. Calpain activity increased in conjunction with ER Ca2+ release. Pretreatment, but not post-treatment, with thapsigargin or cyclopiazonic acid prevented antimycin A-induced cell death. These data demonstrate that extensive ATP depletion signals oncosis through ER Ca2+ release, a sustained increase in Ca2+f and calpain activation. Depletion of ER Ca2+ stores prior to toxicant exposure prevents increases in Ca2+f and oncosis.