Regulation of intracellular free arachidonic acid in Aplysia nervous system.

We have studied the regulation of arachidonic acid (AA) uptake, metabolism, and release in Aplysia nervous system. Following uptake of [3H]AA, the distribution of radioactivity in intracellular and extracellular lipid pools was measured as a function of time in the presence or absence of exogenous AA. The greatest amount of AA was esterified into phosphatidylinositol (relative to pool size). We found that the intracellular free AA pool underwent rapid turnover, and that radioactive free AA and eicosanoids were released at a rapid rate into the extracellular medium, both in the presence and absence of exogenous AA. Most of the released radioactivity originated from phosphatidylinositol. Two pharmacological agents were found to modulate AA metabolism in Aplysia ganglia. The phorbol ester, 12-O-tetradecanoylphorbol 13-acetate, stimulated liberation of AA from phosphatidylinositol and phosphatidylcholine. This resulted in an increase in free internal and secreted AA, an increase in conversion of AA to eicosanoids, and an increase in esterification of AA into triacylglycerol. The half maximal dose for TPA-stimulated AA turnover was 15 nM, and the stimulation was dependent on the presence of extracellular calcium. 4-bromophenacylbromide inhibited the redistribution of radioactivity from phospholipid into triacylglycerol, indicating BPB was acting as a phospholipase inhibitor in Aplysia as it does in other systems. These pharmacological agents, in addition to providing information about the regulation of AA metabolism and release, are useful tools for investigating the physiological function of the rapid turnover of AA in Aplysia nervous system.