Efflux of gamma-aminobutyric acid from and appearance of free arachidonic acid inside synaptosomes.

When synaptosomes were depolarized in the presence of Ca2+, or when Ca2+ was added to synaptosomes pretreated with Ca2+ ionophore (A23187), free arachidonic acid was clearly increased within synaptosomes, and at the same time an efflux of gamma-aminobutyric acid from synaptosomes was observed. Moreover, when synaptosomes labelled with [14C]arachidonic acid were depolarized in the presence of Ca2+, there was a significant decrease in the radioactivity of the fatty acid of phosphatidylinositol and phosphatidylcholine. Exogenously added arachidonic acid, but not other fatty acids, stimulated the efflux of gamma-aminobutyric acid in the absence of Ca2+. These observations suggest that the release of arachidonic acid from phospholipids is an intrinsic part of the biochemical mechanism that modulates the gamma-aminobutyric acid efflux.