Intracellular Ca2+ operates a switch between repair and lysis of streptolysin O-perforated cells

Pore-forming (poly) peptides originating from invading pathogens cause plasma membrane damage in target cells, with consequences as diverse as proliferation or cell death. However, the factors that define the outcome remain unknown. We show that in cells maintaining an intracellular Ca2+ concentration [Ca2+](i) below a critical threshold of 10 mu M, repair mechanisms seal off 'hot spots' of Ca2+ entry and shed them in the form of microparticles, leading to [Ca2+](i) reduction and cell recovery. Cells that are capable of preventing an elevation of [Ca2+](i) above the critical concentration, yet are unable to complete plasma membrane repair, enter a prolonged phase of [Ca2+](i) oscillations, accompanied by a continuous shedding of microparticles. When [Ca2+](i) exceeds the critical concentration, an irreversible formation of ceramide platforms within the plasma membrane and their internalisation drives the dying cells beyond the 'point of no return'. These findings show that the extent of [Ca2+](i) elevation determines the fate of targeted cells and establishes how different Ca2+-dependent mechanisms facilitate either cell survival or death. Cell Death and Differentiation (2009) 16, 1126-1134; doi:10.1038/cdd.2009.30; published online 27 March 2009