Endoplasmic reticulum Ca2+ signaling and calpains mediate renal cell death

The goal of the current study was to determine the roles of ATP content, endoplasmic reticulum (ER) Ca2+ stores, cytosolic free Ca2+ (Ca-f(2+)) and calpain activity in the signaling of rabbit renal proximal tubular (RPT) cell death (oncosis). Increasing concentrations (0.3-10 muM) of the mitochondrial inhibitor antimycin A produced rapid ATP depletion that correlated to a rapid and sustained increase in Ca-f(2+), but not phospholipase C activation. The ER Ca2+-ATPase inhibitors thapsigargin (5 muM) or cyclopiazonic acid (100 muM) alone produced similar but transient increases in Ca-f(2+). Pretreatment with thapsigargin prevented antimycin A-induced increases in Ca-f(2+) and antimycin A pretreatment prevented thapsigargin-induced increases in Ca f. Calpain activity increased in conjunction with ER Ca2+ release. Pretreatment, but not post-treatment, with thapsigargin or cycloplazonic acid prevented antimycin A-induced cell death. These data demonstrate that extensive ATP depletion signals oncosis through ER Ca2+ release, a sustained increase in Ca-f(2+) and calpain activation. Depletion of ER Ca2+ stores prior to toxicant exposure prevents increases in Ca-f(2+) and oncosis.