Pharmacological assessment of M1 muscarinic acetylcholine receptor-Gq/11 protein coupling in membranes prepared from postmortem human brain tissue

Using a selective G alpha(q/11) protein antibody capture guanosine 5'-O-(3-[S-35]thio)triphosphate ([S-35]GTP gamma S) binding approach, it has been possible to perform a quantitative pharmacological examination of the functional activity of the M-1 muscarinic acetylcholine receptor (mAChR) in membranes prepared from human postmortem cerebral cortex. Oxotremorine-M caused a >= 2-fold increase in [S-35] GTP GS-G alpha(q/11) binding with a pEC(50) of 6.06 +/- 0.16 in Brodmann's areas 23 and 25 that was almost completely inhibited by preincubation of membranes with the M-1 mAChR subtype-selective antagonist muscarinic toxin-7. In addition, the orthosteric and allosteric agonists, xanomeline [3(3-hexyloxy-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine] and AC-42 (4-n-butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine hydrogen chloride), increased [S-35]-GTP gamma S-G alpha(q/11) binding, but with reduced intrinsic activities, inducing maximal responses that were 42 +/- 1 and 44 +/- 2% of the oxotremorine-M-induced response, respectively. These data indicate that the M-1 receptor is the predominant mAChR subtype coupling to the G alpha(q/11) G protein in these brain regions and that it is possible to quantify the potency and intrinsic activity of full and partial M-1 mAChR receptor agonists in postmortem human brain using a selective G alpha(q/11) protein antibody capture [S-35]GTP gamma S binding assay.