Fig. 1.

Schematic map of mitochondrial Ca²⁺ transporters. Mitochondria accumulate Ca²⁺ in the matrix via an electrogenic Ca²⁺ uniporter (MCU) that acts to equilibrate Ca²⁺ according the electrochemical gradient generated by the respiratory chain (ETC). Voltage Dependent Anion Channel (VDAC) controls the Ca²⁺ diffusion through the outer mitochondrial membrane (OMM), thus facilitating mitochondrial Ca²⁺ accumulation. As to the efflux pathways, a Na⁺/Ca²⁺ and a H⁺/Ca²⁺ exchangers have been shown to operate. The permeability transition pore (PTP) opening plays different roles: its brief opening could allow rapid Ca²⁺ release, but its long-lasting openings (potentiated by apoptotic stimuli and Ca²⁺ itself) could trigger cell death process. IMS, intermembrane space; IMM, inner mitochondrial membrane.