Article

Nature 454, 722-727 (7 August 2008) | doi:10.1038/nature07139; Received 24 April 2008; Accepted 5 June 2008; Published online 16 July 2008

On the nature of partial agonism in the nicotinic receptor superfamily

Remigijus Lape1, David Colquhoun1 & Lucia G. Sivilotti1

  1. Department of Pharmacology, University College London, Medical Sciences Building, Gower Street, London WC1E 6BT, UK

Correspondence to: David Colquhoun1 Correspondence and requests for materials should be addressed to D.C. (Email: d.colquhoun@ucl.ac.uk).

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Partial agonists are ligands that bind to receptors but produce only a small maximum response even at concentrations where all receptors are occupied. In the case of ligand-activated ion channels, it has been supposed since 1957 that partial agonists evoke a small response because they are inefficient at eliciting the change of conformation between shut and open states of the channel. We have investigated partial agonists for two members of the nicotinic superfamily—the muscle nicotinic acetylcholine receptor and the glycine receptor—and find that the open–shut reaction is similar for both full and partial agonists, but the response to partial agonists is limited by an earlier conformation change ('flipping') that takes place while the channel is still shut. This has implications for the interpretation of structural studies, and in the future, for the design of partial agonists for therapeutic use.

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