Identification of a titratable lysine residue that determines sensitivity of kidney potassium channels (ROMK) to intracellular pH.
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.
Fakler
B
B
Department of Sensory Biophysics, ENT-Hospital of the University of Tübingen, Germany.
Schultz
J H
JH
Yang
J
J
Schulte
U
U
Brandle
U
U
Zenner
H P
HP
Jan
L Y
LY
Ruppersberg
J P
JP
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
D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins; D008239:Lysine; D011188:Potassium