Muscarinic acetylcholine receptors regulation and protein phosphorylation in primary cultures of rat cerebellum.

Exposure of primary cell cultures of rat cerebellum to the muscarinic agonist carbachol led to a 50% loss in apparent muscarinic receptor number detectable in a ligand binding assay using [3H]quinuclidinyl benzilate ([3H]QNB). The loss in [3H]QNB binding was time-dependent with a half-life of 2.9 h. Examination of membrane protein phosphorylation indicated that exposure to carabachol resulted in an increase in the level of phosphorylation of 6 polypeptides. The increased phosphorylation of 3 of these polypeptides, of molecular weights, 75,000, 67,000 and 62,000, followed a similar time-course to that of carbachol-induced loss of receptor binding. These results are consistent with the idea that the muscarinic receptor regulation involves a protein phosphorylation mechanism.