Conversion of the ion selectivity of the 5-HT3A receptor from cationic to anionic reveals a conserved feature of the ligand-gated ion channel superfamily (vol 276, pg 10977, 2001)

The 5-hydroxytryptamine, (5-HT3) receptor is a member of a superfamily of l igand-gated ion channels, which includes nicotinic acetylcholine, gamma -am inobutyric acid, and glycine receptors. The receptors are either cation or anion selective, leading to their distinctive involvement in either excitat ory or inhibitory neurotransmission. Using a combination of site-directed m utagenesis and electrophysiological characterization of homomeric 5-HT3A re ceptors expressed in HEK293 cells, we have identified a set of mutations th at convert the ion selectivity of the 5-HT3A receptor from cationic to anio nic; 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 per meability (P-Cl/P-Na = 12.3, P-Na/P-Cl = 0.08), whereas WT receptors are pr edominantly permeable to sodium (P-Na/P-Cl > 20, P-Cl/P-Na < 0.05). Since t he equivalent mutations have previously been shown to convert <alpha>7 nico tinic acetylcholine receptors from cationic to anionic (Galzi J.-L., Devill ers-Thiery, A, Hussy, N., Bertrand, S. Changeux, J. P., and Bertrand, D. (1 992) Nature 359, 500-505) and, recently, the converse mutations have allowe d the construction of a cation selective glycine receptor (Keramidas, A, Mo orhouse, A. J., French, C. R., Schofield, P. R., and Barry, P. H. (2000) Bi ophys. J. 78, 247-259), it appears that the determinants of ion selectivity represent a conserved feature of the ligand-gated ion channel superfamily.