Nitric oxide modulates muscarinic acetylcholine receptor binding in the cerebral cortex of gerbils

To determine whether nitric oxide (NO) acts as a modulator of muscarinic acetylcholine receptor (mACh-R) function, we performed a radioligand receptor assay using [3H]quinuclidinyl benzylate ([3H]QNB), the NO radical (NO*) donor 3-(2-Hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamin e (NOC7) and a gerbil brain cortical membrane preparation. NOC7 (at 10 microM, 100 microM or 1 mM concentrations) significantly reduced the [3H]QNB binding Kd values (from 0.196 +/- 0.009 nM in the control, to 0.151 +/- 0.013, 0.144 +/- 0.012 and 0.153 +/- 0.007 nM respectively). NOC7 did not alter the displacement curves of atropine or carbachol. Reduction of SH groups with dithiothreitol, in the presence of the NO donor, significantly increased [3H]QNB binding affinity whereas alkylation by N-ethylmaleimide markedly decreased it. The observed enhancing effect on mACh-R binding affinity for [3H]QNB, may reflect conformational changes in the receptors mediated by the NO generated, and these changes might be explained by NO reactions with such groups through conditions supporting redox reactions intrinsic to the NO molecule, similar to those occurring in redox regulatory sites reported for other neurotransmitter pathways in the CNS.