Glucose transport and antilipolysis are differentially regulated by the polar head group of an insulin-sensitive glycophospholipid.

A glycophospholipid has been purified from rat liver membranes, which copurified with an insulin-sensitive glycophospholipid isolated from H35 hepatoma cells. The polar head group of this glycophospholipid, which is a phosphooligosaccharide, was generated by treatment with a phosphatidylinositol-specific phospholipase C from Staphylococcus aureus. There was an "insulin-like" inhibitory effect of this phosphooligosaccharide on isoproterenol-stimulated lipolysis in adipocytes, whereas there was no effect on glucose oxidation under conditions that measure glucose transport. The antilipolytic effect of this phosphooligosaccharide was demonstrated in intact adipocytes. There was a linear correlation between the concentration of phosphooligosaccharide and its antilipolytic effect, the magnitude and time course of which were similar to that obtained with physiological concentrations of insulin. Submaximal concentrations of insulin and phosphooligosaccharide produced an additive antilipolytic effect. The antilipolytic effect of the phosphooligosaccharide was demonstrated only after release of this compound from the precursor glycophospholipid with phosphatidylinositol-specific phospholipase C, and the activity of the phosphooligosaccharide was sensitive to alkali. It is proposed that this phosphooligosaccharide plays a role in mediating certain insulin actions.