Cyclosporin A-sensitive and insensitive mechanisms produce the permeability transition in mitochondria

Cyclosporin A is a potent inhibitor of the mitochondrial permeability transition, possibly by blocking an inner membrane pore through which solute movements occur [Broekemeier et al. (1989) J. Biol. Chem. 264, 7826-7830]. The inhibitory effect of cyclosporin, however, is transient. Trifluoperazine, at concentrations which inhibit the mitochondrial phospholipase A2, also produces a transient inhibition. When both inhibitors are used together, the inhibitory effect is long lasting. These findings suggest that the transition can be caused by two overlapping and/or interactive mechanisms, one dependent on an inner membrane pore and the other on phospholipase A2.