MUSCARINIC RECEPTOR REGULATION OF NG108-15 ADENYLATE-CYCLASE - REQUIREMENT FOR NA+ AND GTP

Abstract

Cholinergic agonists inhibit the basal and PG[prostaglandin]E1-activated adenylate cyclase activity in membranes isolated from the mouse neuroblastoma .times. glioma hybrid cell NG108-15. Inhibition is seen with acetylcholine, acetyl-.beta.-methylcholine and carbachol and is blocked by 2 specific muscarinic antagonists, atropine and quinuclydinylbenzilate. Inhibition of basal and PGE1-activated activity is only partial. Carbachol-directed inhibition has an apparent Km of 6 .mu.M in the presence or absence of PGE1. GTP and Na+ are required for the muscarinic inhibition of basal and PGE1-activated NG108-15 adenylate cyclase. The selectivity seen for monovalent cations (all chloride salts) in this process is Na+ .simeq. Li+ > K+ > choline+ with the ED50 for Na+ .simeq. 40 mM. Of the nucleotides tested, only ITP (and not ATP, UTP or CTP) replaces GTP in this process. GTP at 10 .mu.M represents a saturating nucleotide concentration. Opiate-directed inhibition of NG108-15 adenylate cyclase exhibits a similar requirement for GTP and Na+. Apparently the general transfer of inhibitory information from membrane receptors to adenylate cyclase involves both a Na+ and GTP-sensitive process.