title: Conversion of the ion selectivity of the 5-HT(3a) receptor from cationic to anionic reveals a conserved feature of the ligand-gated ion channel superfamily.
abstract: The 5-hydroxytryptamine(3) (5-HT(3)) receptor is a member of a superfamily of ligand-gated ion channels, which includes nicotinic acetylcholine, gamma-aminobutyric acid, and glycine receptors. The receptors are either cation or anion selective, leading to their distinctive involvement in either excitatory or inhibitory neurotransmission. Using a combination of site-directed mutagenesis and electrophysiological characterization of homomeric 5-HT(3A) receptors expressed in HEK293 cells, we have identified a set of mutations that convert the ion selectivity of the 5-HT(3A) receptor from cationic to anionic; these were substitution of V13'T in M2 together with neutralization of glutamate residues (E-1'A) and the adjacent insertion of a proline residue (P-1') in the M1-M2 loop. Mutant receptors showed significant chloride permeability (P(Cl)/P(Na) = 12.3, P(Na)/P(Cl) = 0.08), whereas WT receptors are predominantly permeable to sodium (P(Na)/P(Cl) > 20, P(Cl)/P(Na) < 0.05). Since the equivalent mutations have previously been shown to convert alpha7 nicotinic acetylcholine receptors from cationic to anionic (Galzi J.-L., Devillers-Thiery, A, Hussy, N., Bertrand, S. Changeux, J. P., and Bertrand, D. (1992) Nature 359, 500-505) and, recently, the converse mutations have allowed the construction of a cation selective glycine receptor (Keramidas, A., Moorhouse, A. J., French, C. R., Schofield, P. R., and Barry, P. H. (2000) Biophys. J. 78, 247-259), it appears that the determinants of ion selectivity represent a conserved feature of the ligand-gated ion channel superfamily.
authors.affiliation: Division of Neurobiology, Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gunthorpe
authors.forename: S C
authors.initials: SC
authors.lastname: Lummis
mesh_terms: D000838:Anions; D002412:Cations; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D011985:Receptors, Serotonin / Q000502:physiology*; D044406:Receptors, Serotonin, 5-HT3; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000838:Anions; D002412:Cations; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3