Acetylcholine and the exchange of inositol and phosphate in brain phosphoinositide.

Previous studies showed that acetylcholine, in the presence of cserine, stimulated the incorporation of P3* into the phospholipidcs in slices of guinea pig brain cortex (2, 3). The major stimulation occurred in phosphoinositidc and in phosphatidic acid, with a lesser stimulation in phosphatidyl choline (3). The incorporation of glycerol-l-U4 into the total glycerophosphatide fraction was not incrcascd under conditions in which P32 incorporation was stimulated (2). The physiological significance of the phospholipide effect in brain cortex slices is not yet understood, although some suggestions have been advanced (4). The present study is primarily concerned with the incorporation of inositol-2-H3 into phosphoinositidc in slices of guinea pig brain cortex incubated in the presence and absence of scetylcholinc. The mdioactivc phosphoinositide isolated from brain cortex slices after incubation in vitro has been shown to be a monophosphoinositidc. Stimulation by acetylcholine of P32 incorporation into this phosphoinositide is accompanied by an equal pcrccntagc of stimulation of inositol-2-H3 incorporation; the incorporation of glycerol-l-C?4 is not stimulated. The incorporation of P32, glycerol-l-C’“, and inositol-2-H” into the other phospholipidcs in the presence and abscncc of acetylcholinc has also been studied.