Ca2+ depletion prevents anoxic death of hepatocytes by inhibiting mitochondrial permeability transition

Removal of Ca2+ from the culture medium or treatment with the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) prevented the killing of rat hepatocytes by anoxia and rotenone, but not by cyanide. Neither manipulation prevented the loss of the mitochondrial membrane potential or the depletion of ATP. A mitochondrial permeability transition (MPT) was demonstrated in digitonin-permeabilized hepatocytes as an increased [3H]sucrose-accessible space sensitive to cyclosporin A (CyA). Ca2+ depletion by either means prevented the MPT measured in intact cells made anoxic or treated with rotenone. In isolated mitochondria deenergized by rotenone, BAPTA-AM prevented the MPT induced by palmitoyl CoA. By contrast, in isolated mitochondria deenergized by cyanide, BAPTA-AM alone did not prevent the MPT. Rather, BAPTA-AM plus CyA were required. Similarly, the killing of cultured hepatocytes by cyanide was prevented by BAPTA-AM plus CyA, but not by either agent alone. The MPT in intact cells treated with cyanide was also prevented by BAPTA-AM plus CyA. These data define a specific requirement for Ca2+ in the killing of hepatocytes that follows the inhibition of electron transport. A model is presented in which the MPT depends on factors that modulate the sensitivity of the permeability transition to the matrix concentration of Ca2+.