Atropine- and scopolamine-resistant subtypes of muscarinic receptors in the rabbit aorta.
Tritiated acetylcholine ([3H]ACh) binds specifically to different muscarinic binding sites in the rabbit aorta. The binding of [3H]ACh to endothelial membranes was displacable by nanomolar concentrations of scopolamine but only by micromolar concentrations of atropine and homatropine. The reverse was true for smooth muscle membranes, i.e. [3H]ACh binding was displacable by nanomolar concentrations of atropine and homatropine but only by micromolar concentrations of scopolamine. Pirenzepine, AF-DX 116 and 4-diphenyl-acetoxy-N-methylpiperidine methobromide (4-DAMP) displaced the binding of [3H]ACh from both tissues in the nano- to micromolar range. Our findings indicate that endothelial receptors are characterised by a high affinity for scopolamine, which possesses a scopine base, and that muscle binding sites have a high affinity for antagonists possessing a tropine base (atropine, homatropine). Both the endothelial and smooth muscle binding sites have a low affinity for AF-DX 116, indicating that they are not of the cardiac type.[1]References
- Atropine- and scopolamine-resistant subtypes of muscarinic receptors in the rabbit aorta. Manjeet, S., Sim, M.K. Eur. J. Pharmacol. (1989) [Pubmed]
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