title: Permeant cations and blockers modulate pH gating of ROMK channels.
abstract: External potassium (K) activates the inward rectifier ROMK (K(ir)1.1) by altering the pH gating of the channel. The present study examines this link between external K and internal pH sensitivity using both the two-electrode voltage clamp and the perfused, cut-open Xenopus oocyte preparation. Elevating extracellular K from 1 mM to 10 mM to 100 mM activated ROMK channels by shifting their apparent pK(a) from 7.2 +/- 0.1 (n = 6) in 1 mM K, to 6.9 +/- 0.02 (n = 5) in 10 mM K, and to 6.6 +/- 0.03 (n = 5) in 100 mM K. At any given internal pH, the number of active ROMK channels is a saturating function of external [K]. Extracellular Cs (which blocks almost all inward K current) also stimulated outward ROMK conductance (at constant 1 mM external K) by shifting the apparent pK(a) of ROMK from 7.2 +/- 0.1 (n = 6) in 1 mM K to 6.8 +/- 0.01 (n = 4) in 1 mM K + 104 mM Cs. Surprisingly, the binding and washout of the specific blocker, Tertiapin-Q, also activated ROMK in 1 mM K and caused a comparable shift in apparent pK(a). These results are interpreted in terms of both a three-state kinetic model and a two-gate structural model that is based on results with KcsA in which the selectivity filter can assume either a high or low K conformation. In this context, external K, Cs, and Tertiapin-Q activate ROMK by destabilizing the low-K (collapsed) configuration of the selectivity filter.
authors.affiliation: Department of Physiology and Biophysics, The Chicago Medical School, North Chicago, Illinois 60064, USA. sackinh@mis.finchcms.edu
authors.forename: H
authors.initials: H
authors.lastname: Sackin
authors.forename: A
authors.initials: A
authors.lastname: Vasilyev
authors.forename: L G
authors.initials: LG
authors.lastname: Palmer
authors.forename: M
authors.initials: M
authors.lastname: Krambis
mesh_terms: D000818:Animals; D001514:Bee Venoms / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D005260:Female; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000737:chemistry* / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D012680:Sensitivity and Specificity; D014982:Xenopus laevis / Q000502:physiology
chemical_list: D001514:Bee Venoms; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins; C029738:tertiapin; D011188:Potassium