Fig. 2.

Mitochondrial calcium loads persist long after activation of the mitochondrial permeability transition. Electron micrographs of typical damaged in situ mitochondria of NMDA-treated cultured hippocampal neurons (upper panel) and calcium-loaded isolated rat brain mitochondria (lower panel). Isolated mitochondria were calcium-loaded in the presence of ATP using a continuous infusion protocol. After the abrupt onset of MPT, mitochondria were further exposed to the protonophore carbonyl cyanide 4-(trifluoromethoxy)-phenylhydrazone (FCCP) and frozen 200 s later (see [75] for experimental details). Both preparations were high pressure-frozen and freeze-substituted in order to preserve the calcium-rich precipitates, whose continued presence demonstrates the longevity of mitochondrial calcium loads. The lower panel also illustrates the variable response of individual mitochondria to calcium challenge. Scale bar = 500 nm (both panels).