Evidence of paired M2 muscarinic receptors
| Autor: | L T, Potter, L A, Ballesteros, L H, Bichajian, C A, Ferrendelli, A, Fisher, H E, Hanchett, R, Zhang |
|---|---|
| Rok vydání: | 1991 |
| Předmět: |
Male
Binding Sites Myocardium Oxotremorine Scopolamine Derivatives Parasympatholytics Rats Inbred Strains Muscarinic Antagonists Buffers N-Methylscopolamine Ligands Tritium Binding Competitive Receptors Muscarinic Guanine Nucleotides Rats Quinuclidinyl Benzilate Kinetics GTP-Binding Proteins Animals Brain Stem |
| Zdroj: | Molecular pharmacology. 39(2) |
| ISSN: | 0026-895X |
| Popis: | Binding assays involving various antagonists, including N-[3H] methylscopolamine, [3H]quinuclidinyl benzilate, AFDX-116, pirenzepine, and propylbenzilylcholine mustard, disclosed only a single population of M2 muscarinic receptors in membranes from the rat "brainstem" (medulla, pons, and colliculi). However, competition curves between N-[3H]methylscopolamine and various agonists, including oxotremorine, cis-dioxolane, and acetylethylcholine mustard, showed approximately equal numbers of guanine nucleotide-sensitive high affinity (H) sites and guanine nucleotide-insensitive low affinity (L) sites. This 50% H phenomenon persisted in different buffers, at different temperatures, after the number of receptors was halved (and, thus, the remaining receptor to guanine nucleotide-binding protein ratio was doubled), after membrane solubilization with digitonin, and when rabbit cardiac membranes were used instead of rat brainstem membranes. Preferential occupation of H sites with acetylethylcholine mustard, and of L sites with quinuclidinyl benzilate or either mustard, yielded residual free receptor populations showing predominantly L and H sites, respectively. Low concentrations of [3H]-oxotremorine-M labeled only H sites, and the Bmax for these sites was 49% of the Bmax found with [3H]quinuclidinyl benzilate plus guanine nucleotide. These and other results are most consistent with the idea that H and L receptor sites exist on separate but dimeric receptor molecules and with the hypothesis that only the H receptors cycle between high and low affinity, depending upon interactions between this receptor molecule and a guanine nucleotide-binding protein. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|