Inositol Hexakisphosphate (Phytic Acid) Enhances Ca²⁺Influx and D‐[³H]Aspartate Release in Cultured Cerebellar Neurons

Abstract: Inositol hexakisphosphate (InsP₆) increased ⁴⁵Ca²⁺uptake in cultured cerebellar granule cells. This increase was concentration dependent (EC₅₀= 20 μM), exhibited slow kinetics, and was present after 5 days of cell maturation in culture. InsP₆ also enhanced D‐[³H]aspartate release in cerebellar granule cells at 11‐12 days in vitro. Stimulation of ⁴⁵Ca²⁺ uptake was also produced by inositol pentakisphos‐phate but not by inositol 1,3,4,5‐tetrakisphosphate. The increase in ⁴⁵Ca²⁺ influx induced by InsP₆ was independent of extracellular Na⁺ and was only partially reduced by the organic calcium channel blocker nifedipine. The intrinsic action of InsP₆ was not affected by competitive or noncompetitive glutamate receptor antagonists. In addition, stimulations of ⁴⁵Ca²⁺ uptake by InsP₆ and glutamate were additive. These data provide evidence that InsP₆ directly activates a specific population of neurons in the CNS.