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Metabolism of phosphatidylinositol in plasma membranes and synaptosomes of rat cerebral cortex: A comparison between endogenous Vs exogenous substrate pools
Author(s) -
Navidi Meena,
MacQuarrie Ronald A.,
Sun Grace Y.
Publication year - 1990
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02544387
Subject(s) - membrane , arachidonic acid , phosphatidylinositol , biochemistry , phospholipase , metabolism , incubation , chemistry , phospholipase a2 , diacylglycerol kinase , phospholipase c , endogeny , synaptosome , phospholipid , enzyme , protein kinase c , signal transduction
The metabolism of phosphatidylinositols (PI) labeled with [ 14 C]arachidonic acid within plasma membranes or synaptosomes was compared to the metabolism of PI prelabeled with [ 14 C]arachidonic acid and added exogenously to the same membranes. Incubation of membranes containing the endogenously‐labeled PI pool in the presence of Ca 2+ resulted in the release of labeled arachidonic acid, as well as a small amount of labeled diacylglycerol. Labeled arachidonic acid was effectively reutilized and returned to the membrane phospholipids in the presence of adenosine triphosphate (ATP), CoA, and lysoPI. Although Ca 2+ promoted the release of labeled diacylglycerol from prelabeled plasma membranes, this amount was only 17% of the maximal release, i.e., release in the presence of deoxycholate and Ca 2+ . This latter condition is known to fully activate the PI‐phospholipase C, and incubation of prelabeled plasma membranes resulted in a six‐fold increase in labeled diacylglycerols. On the other hand, when exogenously labeled PI were incubated with plasma membranes in the presence of Ca 2+ , the labeled diacylglycerols released were 59% of that compared to the fully activated condition. The phospholipase C action was calcium‐dependent, regardless of whether exogenous or endogenous substrates were used in the incubation. In contrast to plasma membranes, intact synaptosomes had limited ability to metabolize exogenous PI even in the presence of Ca 2+ , although the activity of phospholipase C was similar to that in the plasma membranes when assayed in the presence of deoxycholate and Ca 2+ . These results suggest that discrete pools of PI are present in plasma membranes, and that the pool associated with the acyltransferase is apparently not readily accessible to hydrolysis by phospholipase C.