Synthetic inositol 1,3,4,5-tetrakisphosphate analogs and their effect on the binding to microsomal fraction of rat cerebellum

Binding activity of [³H]inositol 1,3,4,5-tetrakisphosphate (InsP₄) was characterized with rat cerebellar membranes. Two types of InsP₄ analog with either the aminobenzoyl or the aminocyclohexanecarbonyl group on the 2nd position of InsP₄ have been synthesized and their effects on the binding activity were also examined. [³H]InsP₄ binding was gradually displaced by increasing amounts of unlabeled InsP₄, with an IC₅₀ of 60-170 nM, depending on the pH values. The binding was sharply increased at acidic pH and millimolar concentrations of Ca²⁺, this being in clear contrast with [³H]InsP₃ binding noted in the same species of tissue. Heparin inhibited the binding, with an IC₅₀ of 1.7, 3 or 20 μg/ml at pH 8.3, 7.2 or 5.0, respectively. Adenine nucleotide inhibited the binding more potently than did [³H]InsP₃ binding. InsP₄ analogs were as effective as InsP₄ in displacing [³H]InsP₄ from rat cerebellar membranes, thereby indicating that the 2nd hydroxl group may not be involved in recognition of InsP₄ by its binding sites.