The subcellular distribution of free fatty acids released during post-decapitative ischemia in rat cerebral cortex.

Abstract

After periods of 5 and 30 min following decapitation, rat cerebral cortices were removed and subcellular fractions were prepared. Fractions P1A (large myelin), P1B (nuclei), P1C (cells and debris), P2A (small myelin), P2B (synaptosomes), P2C (mitochondria), and P3 (microsomes) were isolated. Free fatty acid levels of 1.0 and 1.4 mumol/g tissue were found in the homogenates at the early and late times of ischemia. In the 30-min samples, P1A, P1C, and P2A had relatively high specific contents of total free fatty acids in comparison with other subfractions. At this time P2C was relatively enriched in arachidonate, P1A and P2A were enriched in palmitate, and P2B and P3 were enriched in stearate in comparison with the homogenate. P2C had the highest ratio of polyunsaturates/saturates in its free fatty acid pool. Comparing the 5- and 30-min samples, a large increase in the quantity of free fatty acids was found in fractions P1A and P2A, so that at the later time P1A + P2A contained 60 mol% of the free fatty acid in the total subfractions derived from cerebral cortex. In comparison with the homogenate, the lack of accumulation of free fatty acids in certain membranes known to possess phospholipase activities (e.g., phospholipase A2 in P2C) and the buildup of free fatty acids in P1A and P2A led to the hypothesis that free fatty acids may be migrating outwards from intracellular sites of production and accumulating in the multilamellar structure of myelin.