Mass measurements of inositol(1,4,5)trisphosphate in rat cerebral cortex slices using a radioreceptor assay: effects of neurotransmitters and depolarization.
The specific binding of [3H] and [32P]Ins(1,4,5)P3 to a particulate preparation of bovine adrenal cortex has been used as a radioreceptor assay to determine the concentration of Ins(1,4,5)P3 in agonist- and depolarization-stimulated rat cerebral cortex slices. The resting concentration of Ins(1,4,5)P3 in slices that had been preincubated in a physiological medium was 18.8 +/- 2.6 pmol/mg prot. Carbachol evoked a rapid and dose-related increase in the concentration of Ins(1,4,5)P3. Maximal stimulation (80%) was already seen at the earliest point (10 sec) examined and was maintained for at least 5 min. The EC50 for carbachol was 75 +/- 17 microM and the response was totally suppressed by the muscarinic antagonist atropine. A direct comparison in the same slices was made between mass determinations and [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4)P3 accumulation determined by h.p.l.c. Although an identical time course was observed for cold and radiolabelled Ins(1,4,5)P3, the greater stimulation of [3H]Ins(1,4,5)P3 may indicate changes in specific radioactivity. Of a variety of other receptor agonists studied, only the glutamate receptor agonist quisqualate, and noradrenaline significantly increased the mass of Ins(1,4,5)P3 in cerebral cortical slices. However, depolarizing concentrations of K+ were as effective as carbachol at elevating this second messenger.
Challiss
R A
RA
Department of Pharmacology and Therapeutics, University of Leicester, U.K.
Batty
I H
IH
Nahorski
S R
SR
D000302:Adrenal Cortex / Q000378:metabolism; D000818:Animals; D001923:Brain Chemistry; D015220:Calcium Channels; D002417:Cattle; D002540:Cerebral Cortex / Q000032:analysis / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000032:analysis / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D011984:Sensory Receptor Cells / Q000187:drug effects; D013403:Sugar Phosphates / Q000378:metabolism*
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D018377:Neurotransmitter Agents; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate