Model for plasma membrane repair mediated by secreted lysosomal ASM. Extracellular Ca²⁺ flows into cells through plasma membrane wounds (the diagram shows in red pores formed by insertion of the bacterial toxin SLO). Elevation in the intracellular Ca²⁺ concentration triggers exocytosis of lysosomes. Lysosomal ASM is delivered to the outer leaflet of the plasma membrane, where it converts sphingomyelin into ceramide. Ceramide self-associates into microdomains that bud into the cells, generating endosomes that internalize the lesions and reseal the plasma membrane.