Phospholipase C activities in rat liver plasma membranes depend on the phospholipid composition

Investigations were carried out on the influence of rat liver plasma membranes phospholipid composition on phospholipase C activity using PIP, PIP2, PC and PE as substrates. The membrane phospholipids were modified by incorporation of definite phospholipids with the aid of lipid transfer proteins or after partial delipidation with exogenous phospholipases A2 and C. The results indicated that sphingomyelin inhibited all phospholipase C activities. The incorporation of two different molecular species of phosphatidylcholine did not alter significantly the investigated phospholipase C activities, indicating that membrane fluidity was not essential in this case. Phosphatidylglycerol, phosphatidylserine, phosphatidylinositol and phosphatidylethanolamine served as specific activators of plasma membrane-bound phospholipase C when PIP, PIP2 and PC were used as substrates. However, these four phospholipids inhibited phospholipase C activity towards PE. The role of phosphoinositide-specific phospholipase C in the production of second messengers as well as the eventual biological significance of PC and PE as substrates for phospholipase C is discussed.