Blebbing, free Ca²⁺ and mitochondrial membrane potential preceding cell death in hepatocytes

Cell surface 'blebbing' is an early consequence of hypoxic and toxic injury to cells^1-5. A rise in cytosolic free Ca²⁺ has been suggested as the stimulus for bleb formation^3-5 and the final common pathway to irreversible cell injury^6-9. Here, using digitized low-light video microscopy, we examine blebbing, cytosolic free Ca²⁺, mitochondrial membrane potential and loss of cell viability in individual cultured hepatocytes. Unexpectedly, we found that after 'chemical hypoxia' with cyanide and iodoacetate, cytosolic free Ca²⁺ does not change during bleb formation or before loss of cellular viability. Cell death was precipitated by a sudden breakdown of the plasma membrane permeability barrier, possibly caused by rupture of a cell surface bleb.