II. Biochemical mechanisms in the phosphatidylinositol effect

Abstract

Stimulated labeling of phospholipids from 32Pi is a hallmark of activation of a variety of cell surface receptors. In the case of the central nervous system, the response can reflect muscarinic activation. Recent studies in nerve ending preparations indicate a postsynaptic site of action. Ca2+ is required for the expression of cholinergic stimulation of labeling in nerve ending preparations, but whether it plays a regulatory role is not yet known. While it is inferred that the receptor-ligand interaction leads to increased diacylglycerol availability, its source is not established. In experiments with muscarinic agents and ionophore added to nerve ending preparations, there is a potentiated loss of labeling from prelabeled polyphosphoinositides. It is suggested that phosphodiesteratic cleavage of polyphosphoinositides may be an early consequence of muscarinic receptor activation.