Effects of Acetylcholine on Labeling of Phosphatidate and Phosphoinositides by [32P]Orthophosphate in Nerve Ending Fractions of Guinea Pig Cortex

The effect of acetylcholine on the incorporation of 32Pi into phospholipids was studied in subfractions of guinea pig cerebral cortex obtained by sucrose density fractionation. Incorporation of label into phosphatidic acid and phosphatidylinositol was stimulated approximately 100 and 70%, respectively, by 10-4 m acetylcholine in a nerve ending fraction rich in acetylcholine esterase. The effect was not significant in other subcellular fractions investigated, including a denser nerve ending fraction. This action of acetylcholine was blocked by the addition of atropine but not by tubocurare. Labeling of phosphatidylinositol phosphate and phosphatidylinositol diphosphate was inhibited by about 20% in the presence of 10-4 m acetylcholine. This inhibition was not specific for any of the subfractions and was not affected by the addition of atropine.