Reduced capacity of Ca²+ retention in liver as compared to kidney mitochondria. ADP requirement.

Ca²+ loading in mitochondria promotes the opening of a non-selective transmembrane pathway. Permeability transition is also associated with the interaction of cyclophilin D at the internal surface of the non-specific transmembrane pore. This interaction is circumvented by cyclosporin A and ADP. Our results show that, in the absence of ADP, liver mitochondria were unable to retain Ca²+, they underwent a fast and large amplitude swelling, as well as a rapid collapse of the transmembrane potential. In contrast, in the absence of ADP, kidney mitochondria retained Ca²+, swelling did not occur, and the collapse of the membrane potential was delayed. Ca²+ efflux was reversed by the addition of ADP and cyclosporin A. Our findings indicate that the differences between liver and kidney mitochondria are due to the low association of cyclophilin D to the ADP/ATP carrier found in kidney mitochondria as compared to liver mitochondria.