A new model system for studying the phosphatidylinositol cycle.

An early manifestation of the response of WRK-1 rat mammary tumor cells to vasopressin is an increase in incorporation of (32P)Pi into phospholipids. Incorporation into all classes of phospholipids is stimulated; however, incorporation into phosphatidylinositol (PI) is increased to the greatest degree (3- to 10-fold as compared with 1.3- to 2-fold for the other phospholipids). Furthermore, increased incorporation into PI is accompanied by an increased rate of PI turnover; turnover rates of the other phospholipids are unaffected by vasopressin.