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A cytoplasmic region determines single-channel conductance in 5-HT3 receptors

Nature volume 424, pages 321–324 (2003)Cite this article

Abstract

5-Hydroxytryptamine type 3 (5-HT3) receptors are cation-selective transmitter-gated ion channels of the Cys-loop superfamily1,2,3,4,5,6,7,8,9. The single-channel conductance of human recombinant 5-HT3 receptors assembled as homomers of 5-HT3A subunits, or heteromers of 5-HT3A and 5-HT3B subunits, are markedly different, being 0.4 pS (refs 6, 9) and 16 pS (ref. 7), respectively. Paradoxically, the channel-lining M2 domain of the 5-HT3A subunit would be predicted to promote cation conduction, whereas that of the 5-HT3B subunit would not7. Here we describe a determinant of single-channel conductance that can explain these observations. By constructing chimaeric 5-HT3A and 5-HT3B subunits we identified a region (the ‘HA-stretch’)10 within the large cytoplasmic loop of the receptor that markedly influences channel conductance. Replacement of three arginine residues unique to the HA-stretch of the 5-HT3A subunit by their 5-HT3B subunit counterparts increased single-channel conductance 28-fold. Significantly, ultrastructural studies of the Torpedo nicotinic acetylcholine receptor11 indicate that the key residues might frame narrow openings that contribute to the permeation pathway. Our findings solve the conundrum of the anomalously low conductance of homomeric 5-HT3A receptors and indicate an important function for the HA-stretch in Cys-loop transmitter-gated ion channels.

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Figure 1: The strategy employed to identify the domain of the 5-HT3B subunit conferring enhanced single-channel conductance on heteromeric (5-HT3A and 5-HT3B) and on homomeric (5-HT3A) receptors.
Figure 2: Identification of the domain of the 5-HT3B subunit responsible for the enhanced conductance of hetero-oligomeric compared with homo-oligomeric 5-HT3 receptors.
Figure 3: Conserved arginine residues within the HA-stretch of the 5-HT3A receptor subunit influence single-channel conductance.

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Acknowledgements

We thank M.L.J. Ashford for constructive comments on an earlier version of this manuscript. This work was supported by grants from the Wellcome Trust and Tenovus Tayside to J.A.P. and J.J.L. and from the Anonymous Trust to J.A.P.

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Authors and Affiliations

  1. Neurosciences Institute, Department of Pharmacology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, DD1 9SY, Dundee, UK

    Stephen P. Kelley, James I. Dunlop, Jeremy J. Lambert & John A. Peters

  2. The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, Maryland, 20850, USA

    Ewen F. Kirkness

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  1. Stephen P. Kelley
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Correspondence to John A. Peters.

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Kelley, S., Dunlop, J., Kirkness, E. et al. A cytoplasmic region determines single-channel conductance in 5-HT3 receptors. Nature 424, 321–324 (2003). https://doi.org/10.1038/nature01788

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