Evidence for a Ca2+‐independent hydrolysis of phosphatidylinositol 4,5‐bisphosphate in neuron‐like cell line NG108‐15 cells

The addition of bradykinin to 32Pi-labeled neuroblastoma X glioma hybrid NG108-15 cells caused a substantial loss of radioactivity from phosphatidylinositol 4,5-bisphosphate (PI-4,5-P2). The bradykinin-induced hydrolysis of PI-4,5-P2 was almost equally observed even when extracellular Ca2+ was depleted with EGTA (100 microns). On the other hand, high K+ depolarization of the cells, which allows Ca2+ influx through voltage-dependent Ca2+ channels, failed to induce any significant decrease in the radioactivity of PI-4,5-P2. These data indicate that the bradykinin-stimulated PI-4,5-P2 hydrolysis in NG108-15 cells is independent of extracellular Ca2+ and also that PI-4,5-P2 hydrolysis is not stimulated by an elevation of intracellular Ca2+ concentration.