An increased incorporation of fatty acid into triacylglycerols of neuronal nuclei in vitro in the presence of CMP and EGTA

Abstract

Neuronal nuclei (N1) were isolated from cerebral cortices of 15-day-old rabbits. With the addition of both EGTA and CMP the incorporation of radioactive oleate into N1 triacylglycerols in vitro (in the presence of ATP, CoA, and MgCl2) was increased threefold. The same large increase could not be achieved using citrate or EDTA in the presence of CMP or using AMP, UMP, or TMP in the presence of EGTA. The increased labelling of N1 triacylglycerols could be greatly reduced when CDP-choline was added to incubations containing EGTA and CMP. Levels of endogenous N1 diacylglycerols increased threefold following a 10-min incubation in the presence of buffer (pH 7.4) and MgCl2, when CMP and EGTA were also added. Of the major N1 phospholipids, phosphatidylcholine was most similar in fatty acid composition to the enlarged endogenous diacylglycerol pool. The rate of formation of oleoyl-CoA in fraction N1 was not significantly changed by the presence of EGTA and CMP. Rates of triacylglycerol labelling could only be modestly increased when EGTA and CMP were added to incubations containing N1 samples with artificially enlarged endogenous diacylglycerol pools (produced by phospholipase C preincubations). It is suggested that EGTA, as a Ca2+ chelator, and CMP, as a substrate, may allow an enhanced diacylglycerol production mediated by the back reaction of cholinephosphotransferase in N1. The endogenous N1 diacylglycerols produced in the absence of EGTA and CMP may come from another metabolic route.