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Allosteric interactions among agonists and antagonists at 5-hydroxytryptamine3 receptors
D W Bonhaus1, E Stefanich, D N Loury
1Department of Neurosciences, Syntex Discovery Research, Palo Alto, California 94303, USA.
Journal of Neurochemistry
|July 1, 1995
Summary
Multiple binding sites on serotonin 5-HT3 receptors show cooperative interactions. Agonists can enhance binding affinity at unoccupied sites, influencing ligand interactions on both native and cloned receptors.
Area of Science:
- Pharmacology
- Neuroscience
- Molecular Biology
Background:
- Cooperation among agonists suggests multiple binding sites on 5-hydroxytryptamine3 (5-HT3) receptors.
- Understanding these interactions is crucial for receptor characterization.
Purpose of the Study:
- To characterize the binding sites and their interactions on native and cloned 5-HT3 receptors.
- To investigate the influence of agonists and antagonists on receptor binding affinities.
Main Methods:
- Radioligand binding assays using [3H]RS-42358, [3H]granisetron, and [3H]mCPG.
- Characterization of competitive antagonist affinities.
- Analysis of agonist and antagonist dissociation rates in the presence of varying ligands.
Main Results:
- Competitive antagonist affinities were consistent across different radioligands.
- Agonist affinities were significantly higher when using [3H]mCPG as the radioligand.
- Agonists (5-HT, 2-methyl-5-HT) slowed the dissociation of certain radioligands ([3H]mCPG, [3H]RS-42358, [3H]RS-25259), but not [3H]granisetron.
Conclusions:
- Data support positive cooperation among multiple binding sites on 5-HT3 receptors.
- Agonists can modulate the interaction of some, but not all, antagonists with the receptor.
- These findings provide deeper insight into the complex allosteric modulation of 5-HT3 receptors.