Cyclosporin A-insensitive permeability transition in brain mitochondria: inhibition by 2-aminoethoxydiphenyl borate.

The mitochondrial permeability transition pore (PTP) may operate as a physiological Ca2+ release mechanism and also contribute to mitochondrial deenergization and release of proapoptotic proteins after pathological stress, e.g. ischemia/reperfusion. Brain mitochondria exhibit unique PTP characteristics, including relative resistance to inhibition by cyclosporin A. In this study, we report that 2-aminoethoxydiphenyl borate blocks Ca2+-induced Ca2+ release in isolated, non-synaptosomal rat brain mitochondria in the presence of physiological concentrations of ATP and Mg2+. Ca2+ release was not mediated by the mitochondrial Na+/Ca2+ exchanger or by reversal of the uniporter responsible for energy-dependent Ca2+ uptake. Loss of mitochondrial Ca2+ was accompanied by release of cytochrome c and pyridine nucleotides, indicating an increase in permeability of both the inner and outer mitochondrial membranes. Under these conditions, Ca2+-induced opening of the PTP was not blocked by cyclosporin A, antioxidants, or inhibitors of phospholipase A2 or nitric-oxide synthase but was abolished by pretreatment with bongkrekic acid. These findings indicate that in the presence of adenine nucleotides and Mg2+,Ca2+-induced PTP in non-synaptosomal brain mitochondria exhibits a unique pattern of sensitivity to inhibitors and is particularly responsive to 2-aminoethoxydiphenyl borate.