摘要：Abstract We report reversible Ca2+-induced Ca2+ release from mitochondria, which takes the form of Ca2+ spikes. Mitochondrial Ca2+ spiking is an all-or-none process with a threshold dependence on both the frequency and the amplitude of the Ca2+ pulses used as stimuli. This spiking relies on the transient operation of the mitochondrial permeability transition pore, and is initiated — in a threshold-dependent manner — with inositol-triphosphate-mediated Ca2+ responses in permeabilized cells. Evidence that mitochondrial Ca2+-induced Ca2+ release contributes to inositol-triphosphate-mediated Ca2+ responses in intact cells is also reported.