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Ca 2+ ‐Independent, Ca 2+ ‐Dependent, and Carbachol‐ Mediated Arachidonic Acid Release from Rat Brain Cortex Membrane
Author(s) -
Strosznajder Joanna,
Samochocki Marek
Publication year - 1991
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1991.tb08280.x
Subject(s) - carbachol , egta , phospholipase c , arachidonic acid , liberation , chemistry , phospholipase a2 , phosphatidylinositol , phosphatidic acid , mastoparan , bradykinin , calcium , biochemistry , phospholipid , endocrinology , receptor , biology , enzyme , g protein , membrane , signal transduction , in vitro , organic chemistry
Synaptoneurosomes obtained from the cortex of rat brain prelabeled with [ 14 C] arachidonic acid ([ 14 C]AA) were used as a source of substrate and enzyme in studies on the regulation of AA release. A significant amount of AA is liberated in the presence of 2 m M EGTA, independently of Ca 2+ , primarily from phosphatidic acid and polyphosphoinositides (poly‐PI). Quinacrine, an inhibitor of phospholipase A 2 (PLA 2 ), suppressed AA release by about 60% and neomycin, a putative inhibitor of phospholipase C(PLC), reduced AA release by about 30%. An additive effect was exhibited when both inhibitors were given together. Ca 2+ activated AA release. The level of Ca 2+ present in the synaptoneurosomal preparation (endogenous level) and 5 μ M CaC1 2 enhance AA liberation by approximately 25%, whereas 2 m M CaC1 2 resulted in a 50% increase in AA release relative to EGTA. The source for Ca 2+ ‐dependent AA release is predominantly phosphatidylinositol (PI); however, a small pool may also be liberated from neutral lipids. Carbachol, an agonist of the cholinergic receptor, stimulated Ca 2+ ‐dependent AA release by about 17%. Bradykinin enhanced the effect of carbachol by about 10–15%. This agonist‐mediated AA release occurs specifically from phosphoinositides (PI + poly‐PI). Quinacrine almost completely suppresses calcium‐ and carbachol‐mediated AA release. Neomycin inhibits this process by about 30% and totally suppresses the effect of bradykinin. Our results indicate that both phospholipases PLA 2 and PLC with subsequent action of DAG lipase are responsible for Ca 2+ ‐ independent AA release. Ca 2+ ‐dependent and carbachol‐mediated AA liberation occurs mainly as the result of PLA 2 action. A small pool of AA is probably also released by PLC, which seems to be exclusively responsible for the effect of bradykinin.