The involvement of cyclosporin A binding proteins in regulating and uncoupling mitochondrial energy transduction.

The uncoupling of mitochondrial energy transduction by excess Ca2+ may be a factor in the pathogenesis of tissue injury brought about by energy deprivation, for example, in ischaemia. In isolated mitochondria the lesion appears as a large, 20 A, pore in the inner membrane. The pore is blocked potently by the immunosuppressant cyclosporin A. Cyclosporin A also markedly retards collapse of the mitochondrial inner membrane potential in energy-deprived (respiration-inhibited) cardiomyocytes as judged by changes in rhodamine 123 fluorescence, and prolongs cell viability. A potential mitochondrial target for cyclosporin A is the matrix protein cyclophilin. Purified cyclophilin activates the respiratory chain of submitochondrial particles. This might reflect not only a physiological function of this protein, but also a component involved in the generation of the 20 A pore under pathological conditions.