Specific binding of [3H]inositol trisphosphate to rat cerebral cortical microsomal membranes.

Specific binding sites for inositol-(1,4,5)-trisphosphate (IP3) were demonstrated in rat cerebral cortical microsomal membranes using [3H]IP3 as the ligand. The binding was displaceable (IC50 for IP3 = 28 nM), high affinity (Kd = 20 nM) and saturable (Bmax = 7.75 pmol/mg protein). Kinetic studies showed an extremely rapid time-course of [3H]IP3 binding with half-maximal binding achieved in less than 1 min and equilibrium binding was attained by around 5 min. These results are in accord with the proposed function of IP3 in mobilizing intracellular calcium from endoplasmic reticulum.