Anomalous binding of [3H]N-methylscopolamine to rat brain muscarinic receptors

Jong Hwa Lee, Esam E. El-Fakahany

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16 Scopus citations


In the present studies, we investigate the binding properties of [3H]quinuclidinyl benzilate ([3H]QNB) and [3H]N-methylscopolamine ([3H]NMS) to muscarinic acetylcholine receptors (mAChR) in rat brain homogenates. Our results indicate that the hydrophilic receptor ligand, [3H]NMS, is able to interact with high affinity only with a fraction of the receptor sites available to the lipophilic ligand, [3H]QNB. Furthermore, displacement experiments demonstrated that while both unlabeled QNB and NMS displaced [3H]NMS binding according to the law of mass-action, NMS, but not QNB, displayed binding heterogeneity when [3H]QNB was used as a ligand. Our data suggest that the lipid solubility of a particular mAChR ligand might play an important role in determining its profile of binding to the receptor.

Original languageEnglish (US)
Pages (from-to)263-266
Number of pages4
JournalEuropean Journal of Pharmacology
Issue number2
StatePublished - Apr 2 1985
Externally publishedYes

Bibliographical note

Funding Information:
This research was supported in part by a UMAB graduate school research award, an NIH Biomedical Research Support grant 2-507-440S770-05 and a grant from the National Science Foundation (BNS-84-06357). The authors are grateful to Ms. Anita Saulsbury and Mrs. Pat Tretter for typing the manuscript, and to Mr. Michael Gentry for his invaluable technical assistance.


  • Muscarinic receptors
  • Receptor heterogeneity
  • [H]N-Methylscopolamine
  • [H]Quinuclidinyl benzilate


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