title: A single residue in the S6 transmembrane domain governs the differential flecainide sensitivity of voltage-gated potassium channels.
abstract: Flecainide has been used to differentiate Kv4.2-based transient-outward K(+)-currents (flecainide-sensitive) from Kv1.4-based (flecainide-insensitive). We found that flecainide also inhibits ultrarapid delayed rectifier (I(Kur)) currents in Xenopus laevis oocytes carried by Kv3.1 subunits (IC(50), 28.3 +/- 1.3 microM) more strongly than Kv1.5 currents corresponding to human I(Kur) (IC(50), 237.1 +/- 6.2 microM). The present study examined molecular motifs underlying differential flecainide sensitivity. An initial chimeric approach pointed to a role for S6 and/or carboxyl-terminal sites in Kv3.1/Kv1.5 sensitivity differences. We then looked for homologous amino acid residues of the two sensitive subunits (Kv4.2 and Kv3.1) different from homologous residues for insensitive subunits (Kv1.4 and Kv1.5). Three candidate sites were identified: two in the S5-S6 linker and one in the S6 segment. Mutation of the proximal S5-S6 linker site failed to alter flecainide sensitivity. Mutation at the more distal site in Kv1.5 (V481L) modestly increased sensitivity, but the reciprocal Kv3.1 mutation (L401V) had no effect. S6 mutants caused marked changes: flecainide sensitivity decreased approximately 8-fold for Kv3.1 L422I (IC(50), 213 +/- 9 microM) and increased approximately 7-fold for Kv1.5 I502L (IC(50), 35.6 +/- 1.9 microM). Corresponding mutations reversed flecainide sensitivity of Kv1.4 and Kv4.2; L392I decreased Kv4.2 sensitivity by approximately 17-fold (IC(50) of 37.4 +/- 6.9 to 628 +/- 36 microM); I547L increased Kv1.4 sensitivity by approximately 15-fold (IC(50) of 706 +/- 37 to 40.9 +/- 7.3 microM). Our observations indicate that the flecainide sensitivity differences among these four voltage-gated K(+)-channels are determined by whether an isoleucine or a leucine is present at a specific amino acid location.
authors.affiliation: Research Center, Montreal Heart Institute, 5000 Belanger St E, Montreal, Quebec, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Herrera
authors.forename: Aida
authors.initials: A
authors.lastname: Mamarbachi
authors.forename: Manuel
authors.initials: M
authors.lastname: Simoes
authors.forename: Lucie
authors.initials: L
authors.lastname: Parent
authors.forename: Rémy
authors.initials: R
authors.lastname: Sauvé
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wang
authors.forename: Stanley
authors.initials: S
authors.lastname: Nattel
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D005260:Female; D005424:Flecainide / Q000494:pharmacology*; D007532:Isoleucine / Q000737:chemistry / Q000235:genetics; D051666:Kv1.5 Potassium Channel; D007930:Leucine / Q000737:chemistry / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry* / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry* / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D051670:Shaw Potassium Channels; D014982:Xenopus laevis
chemical_list: D001426:Bacterial Proteins; D051666:Kv1.5 Potassium Channel; D008565:Membrane Proteins; D009479:Neuropeptides; D024642:Potassium Channels, Voltage-Gated; D051670:Shaw Potassium Channels; D007532:Isoleucine; D007930:Leucine; D005424:Flecainide