SPECIFICITY OF POLYUNSATURATED FATTY-ACID RELEASE FROM RAT-BRAIN SYNAPTOSOMES

Release of specific polyunsaturated fatty acids from cell membranes ma y have a significant implication in biological function, considering t he involvement of various fatty acids in cell signal transduction. In the present study, release of polyunsaturated fatty acids from rat bra in synaptosomes by endogenous synaptosomal lipase activity was examine d in comparison to that by cobra venom phospholipase A(2) (Naja naja n aja). Cobra venom phospholipase A(2) (Naja naja naja) preferentially h ydrolyzed docosahexaenoic acid (22:6n-3) from both synaptosomes and li pid mixtures containing similar classes of lipids commonly found in th e brain. Arachidonic acid (20:4n-6) and oleic acid (18:1n-9) were also hydrolyzed; however, monoene species was hydrolyzed slower than were polyenoic species in synaptosomes. Phosphatidylethanolamine was the mo st preferred phospholipid class for release of 22:6n-3 fatty acid from both lipid mixtures and synaptosomes. In contrast to hydrolysis by co bra venom phospholipase A(2), endogenous synaptosomal lipase activity preferentially hydrolyzed 20:4n-6 from rat brain synaptosomes, despite the high abundance of 22:6n-3 in synaptosomal membranes. Preferential release of 20:4n-6 was observed over a wide range of pH values and ca lcium concentrations. Synaptosomal 22:6 species appeared to be resista nt to hydrolysis even after stimulation with various agents such as ph orbolmyristate, suggesting that physiological importance of 22:6n-3 in neuronal membranes may not be as the release fatty acid.