Vasopressin and epinephrine stimulation of phosphatidylinositol breakdown in the plasma membrane of rat hepatocytes

Hepatocytes obtained from rats injected 18 hours previously with tritiated inositol showed significant phosphatidylinositol breakdown after treatment with 20 mU/ml vasopressin or 10 uM epinephrine. Vasopressin produced only a 4.7% and 7.4% decrease in breakdown of total phosphatidylinositol at 5 and 15 minutes. The subcellular localization of vasopressin and epinephrine induced phosphatidy linositol breakdown was examined in prelabeled hepatocytes incubated with 20 mU/ml vasopressin or 10 uM epinephrine for 5 minutes. There was an appreciable loss (16 to 19%) of labeled phosphatidylinositol from the plasma membrane of isolated hepatocytes exposed to epinephrine or vasopressin for 5 minutes. There was no significant breakdown of the labeled phosphatidylinositol present in endoplasmic reticulum. These results indicate that vasopressin and epinephrine stimulate phosphatidylinositol breakdown in the plasma membrane after activation of cell surface receptors.