Inositol phosphates in receptor-mediated cell signaling: metabolic origins and interrelationships

We have investigated the metabolic interrelationships of the major inositol phosphates in vasopressin-stimulated WRK 1 mammary tumor cells which were labeled to equilibrium with 14C]inositol and briefly, just prior to stimulation, with 3H]inositol. A comparison of the 3H/14C ratios of these compounds with those of the cellular inositol lipids suggests that most of the known inositol mono-, bis-, tris-, and tetrakis-phosphates are derived from precursors with turnover rates similar to those of these lipids. However, Ins(3,4,5,6)P4 (which is the major inositol tetrakisphosphate to accumulate in stimulated WRK 1 cells), Ins(1,3,4,5,6)P5, and InsP6 had 3H/14C ratios of 0 in this experiment, indicating that they must have a different metabolic origin.