NEUROTRANSMITTER AND DEPOLARIZATION-STIMULATED ACCUMULATION OF INOSITOL 1,3,4,5-TETRAKISPHOSPHATE MASS IN RAT CEREBRAL-CORTEX SLICES

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 lns (1,3,4,5)P4 isomer, compared with several other inositol poly phosphates, 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)PP4 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 Copyright © 1990, Wiley Blackwell. All rights reserved