title: Identification of a titratable lysine residue that determines sensitivity of kidney potassium channels (ROMK) to intracellular pH.
abstract: Potassium (K+) homeostasis is controlled by the secretion of K+ ions across the apical membrane of renal collecting duct cells through a low-conductance inwardly rectifying K+ channel. The sensitivity of this channel to intracellular pH is particularly high and assumed to play a key role in K+ homeostasis. Recently, the apical K+ channel has been cloned (ROMK1,2,3 = Kir1.1a, Kir1.1b and Kir1.1c) and the pH dependence of ROMK1 was shown to resemble closely that of the native apical K+ channel. It is reported here that the steep pH dependence of ROMK channels is determined by a single amino acid residue located in the N-terminus close to the first hydrophobic segment M1. Changing lysine (K) at position 80 to methionine (M) removed the sensitivity of ROMK1 channels to intracellular pH. In pH-insensitive IRK1 channels, the reverse mutation (M84K) introduced dependence on intracellular pH similar to that of ROMK1 wild-type. A detailed mutation analysis suggests that a shift in the apparent pKalpha of K80 underlies the pH regulation of ROMK1 channels in the physiological pH range.
authors.affiliation: Department of Sensory Biophysics, ENT-Hospital of the University of Tübingen, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Fakler
authors.forename: J H
authors.initials: JH
authors.lastname: Schultz
authors.forename: J
authors.initials: J
authors.lastname: Yang
authors.forename: U
authors.initials: U
authors.lastname: Schulte
authors.forename: U
authors.initials: U
authors.lastname: Brandle
authors.forename: H P
authors.initials: HP
authors.lastname: Zenner
authors.forename: L Y
authors.initials: LY
authors.lastname: Jan
authors.forename: J P
authors.initials: JP
authors.lastname: Ruppersberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D005260:Female; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000737:chemistry*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry*; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D014982:Xenopus laevis
chemical_list: D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins; D008239:Lysine; D011188:Potassium