[Effect of insulin on inositol-phospholipid metabolism in isolated rat fat cells]

The effects of insulin on the incorporation of [32P]Pi was studied in isolated rat fat cells. When the cells were incubated with insulin and [32P]Pi, a novel radioactive phospholipid, which migrated slower than phosphatidylinositol 4,5-bisphosphate, was detected on thin layer chromatography. The effect of insulin was both dose- and time-dependent. Pretreatment of insulin with anti-insulin antibody or the cells with anti-insulin receptor sodium vanadate stimulated synthesis of this phospholipid in rat adipocytes. These findings indicate that the synthesis of this phospholipid is stimulated through the insulin receptors. The radioactivity of this phospholipid was recovered in the water phase after deacylation with mild alkaline treatment. When extracted lipid were applied to a silicic acid column, the radioactivity of this phospholipid was eluted with methanol, but not with chloroform. This phospholipid coincided with the product of [32P]-phosphatidylinositol 4-phosphate treated with phospholipase A2 on thin layer chromatography. Quinacrine, a phospholipase A2 inhibitor, suppressed the incorporation of [32P]Pi into this phospholipid on dose dependently. This suggests that this phospholipid is lyso-from. suggests that this phospholipid is lyso-from. Insulin stimulated similarly the incorporation of [3H]myo-inositol into this phospholipid. It indicates that this is an inositol phospholipid. Under the same condition, insulin also stimulated the synthesis of this inositol phospholipid in isolated rat hepatocytes, but not in mouse macrophage. It is possible that this reaction is common in insulin target organ.