Specific binding sites for inositolhexakisphosphate in brain and anterior pituitary.

[3H]Inositolhexakisphosphate (InsP6) binds to a single population of specific and saturable recognition sites in membranes prepared from cerebral hemispheres, anterior pituitaries, or cultured cerebellar neurons. Binding is temperature and pH dependent, exhibits slow association and dissociation kinetics, and differentiates among various inositolpolyphosphates (InsP6 is much more potent than inositol-1,3,4,5,6-pentakis- and inositol-1,3,4,5-tetrakisphosphate, whereas inositol-1,4,5-trisphosphate is inactive as a displacer). In membranes from cerebral hemispheres, saturation analysis reveals a KD value of 33 +/- 4 nM and a maximal density (Bmax) of 152 +/- 23 pmol/mg of protein. Both affinity and density of [3H]InsP6 binding are lower in membranes from anterior pituitaries. In cultured cerebellar neurons, micromolar concentrations of divalent cations enhance both [3H]InsP6 binding and InsP6-stimulated 45Ca2+ uptake, suggesting that activation of specific receptors may be involved in the stimulation of 45Ca2+ uptake produced by InsP6. These data support the recent view that InsP6, as other inositolpolyphosphates, may act as a signal molecule in excitable cells.