Increased formation of phosphatidic acid induced with vasopressin or Ca2+ ionophore A23187 in rat hepatocytes

The effects of vasopressin and Ca2+ ionophore A23187 on phospholipid metabolism were investigated in rat hepatocytes. Vasopressin stimulated the incorporation of 32P]Pi into phosphatidic acid within 2 min but then it returned to control level after 10 min. On the other hand, the stimulation of the incorporation of 32P]Pi into phosphatidylinositol continued with incubation times up to 20 min. The Ca2+ ionophore A23187 also increased the 32P-labeling in phosphatidic acid, although it had no effect on 32P]Pi incorporation into phosphatidylinositol. Concerning the incorporation of 3H]glycerol, vasopressin did not enhance its incorporation into phosphatidic acid and phosphatidylinositol. The Ca2+ ionophore A23187 increased the incorporation into phosphatidic acid without significant effects on that into phosphatidylinositol. In the hepatocytes prelabeled with 3H]arachidonic acid, stimulated degradation of phosphatidylinositol with the addition of vasopressin and resultant formation of phosphatidic acid were observed within 5 min. The transient accumulation of diacylglycerol, the product of phosphatidylinositol hydrolysis, also occurred within 5 min with vasopressin. On the other hand, with the Ca2+ inophore A23187, stimulated degradation of triacylglycerol to diacylglycerol and the consequent formation of phosphatidic acid were observed. The Ca2+ ionophore A23187 caused a significant release of free 3H]arachidonic acid, although vasopressin had no effect.