RELEASE OF MITOCHONDRIAL ASPARTATE-AMINOTRANSFERASE (MAST) FOLLOWING TRANSIENT FOCAL CEREBRAL-ISCHEMIA SUGGESTS THE OPENING OF A MITOCHONDRIAL PERMEABILITY TRANSITION PORE

The present experiments were undertaken to study if ischemia and reper fusion in the brain are accompanied by a mitochondrial permeability tr ansition (MPT), leading to the release of mitochondrial proteins into the cytosol. The protein studied was the mitochondrial isoform of aspa rtate aminotransferase (mAST). In vitro experiments showed that isolat ed brain mitochondria exposed to calcium (50 mu M) and phosphate (0.5 mM) displayed rapidly developing swelling, as evidenced by a change in light scattering at 540 nm. The swelling which could be reversal by c helation of external calcium, was associated with release of mAST. Foc al ischemia of 2 h duration was induced by occlusion of one middle cer ebral artery (MCA) by an intraluminal filament technique. The ischemia gave rise to a marked decrease in respiratory control ratio (RCR) of mitochondria in the homogenate. The RCR recovered partly after 1 h of recirculation, but decrease again after 4 h. The mAST in the cytosolic fraction did not change at the end of the ischemia, but increased sig nificantly after 1 h of recirculation in the focus of the lesion, but not in the penumbra. Little further change occurred thereafter (4 h). It is concluded that in densely ischemic areas, recirculation yields r apidly developing dysfunction of the inner mitochondrial membrane, wit h release of mitochondrial proteins.