The formation of plasma membrane blebs in hepatocytes exposed to agents that increase cytosolic Ca2+ is mediated by the activation of a non-lysosomal proteolytic system.

Exposure of isolated hepatocytes to extracellular ATP, cystamine or ionophore A23187 was associated with an increase in cytosolic Ca2+ concentration, a stimulation of intracellular proteolysis, and the appearance of plasma membrane blebs which preceded the loss of cell viability. Both bleb formation and cell killing were prevented when inhibitors of Ca2+-activated neutral proteases, such as antipain or leupeptin, were included in the incubation medium, whereas inhibitors of lysosomal proteases had no effect. Thus, the activation of a Ca2+-dependent, non-lysosomal proteolytic system appears to be responsible for the plasma membrane blebbing and, ultimately, the cytotoxicity associated with treatment of hepatocytes with agents that disrupt intracellular Ca2+ homeostasis.