Pharmacology characterization of guanine nucleotide exchange reactions in membranes from Cho cells stably transfected with human muscarinic receptors m1–m4

https://doi.org/10.1016/0024-3205(93)90301-IGet rights and content

Abstract

We have studied muscarinic agonist stimulated [35S]GTPγS binding and [γ32P]GTP hydrolysis (GTPase) in membranes from CHO cells stably transfected with human muscarinic m1–m4 receptors, ‘Full’ agonists were at least 10-fold more potent at m2 & m4 receptors at m1 & m3. This pattern was less marked with ‘partial” agonists, which has a greater maximal effect at m2 & m4 than at m1 & m3. McN-A343 uniquely was more potent and efficacious at m4 than at m2 receptors. Antagonist affinity constanats were estimated by fitting the data from inhibition curves directly to the Schild model. Antagonist affinity estimates were very similar to those measured earlier in binding studies using animal tissues, and confirmed a small degree of m4 selectively for tropicamide and secoverine. The receptor subtypes activated more than one G-protein subtype; m2 & m4 receptors activated only pertussis (PTX) sensitive G-protein, while m1 & m3 couples to both PTX sensitive and insensitive G-protein. Acetylcholine (ACh) was more potent in stimulating guanine nucleotide exchange in PTX-treated m1 cells than in control.

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