Neurotransmitter and Depolarization-Stimulated Accumulation of Inositol 1,3,4,5-Tetrakisphosphate Mass in Rat Cerebral Cortex Slices

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Abstract
[32P]Inositol 1,3,4,5-tetrakisphosphate ([32P]Ins(1,3,4,5)P4) binds to a rat cerebellar membrane site with high affinity (KD = 2.8 .+-. 0.6 nM) and low capacity (Bmax = 176 .+-. 34 fmol/mg of protein). Evidence for a low-affinity site (KD = 164 .+-. 48 nM) was also apparent. The high-affinity site displayed marked specificity for the Ins(1,3,4,5)P4 isomer, compared with several other inositol polyphosphates, and has been used as the basis of a radioreceptor assay for Ins(1,3,4,5)P4 in extracts of rat cerebral cortex slices. The resting Ins(1,3,4,5)P4 concentration (1.89 .+-. 0.11 pmol/mg of protein) in the slices was rapidly and dramatically increased by carbachol and quisqualate. K+ depolarization of cerebral cortex slices also stimulated Ins(1,3,4,5)P4 accumulation, with at least 50% of the response being sensitive to atropine, a result indicating that muscarinic receptor stimulation by released acetylcholine contributes significantly to the K+ effect.

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