Inositol hexakisphosphate stimulates 45Ca2+ uptake in anterior pituitary cells in culture

Inositol hexakisphosphate (InsP6) is thought to act as an intracellular signal molecule in the central nervous system. We report that InsP6 stimulates 45Ca2+ uptake in cultured anterior pituitary cells. This effect is concentration-dependent, is mimicked by inositol-pentakis phosphate (InsP5) but not by inositol-tetrakis phosphate (InsP4), is present after 2 min of incubation, is independent of extracellular Na+ and insensitive to nifedipine and verapamil. These results suggest that InsP6, a putative metabolite of the inositol cycle, may regulate transmembrane mechanism in the pituitary.