title: Selectivity and interactions of Ba2+ and Cs+ with wild-type and mutant TASK1 K+ channels expressed in Xenopus oocytes.
abstract: The acid-sensitive K(+) channel, TASK1 is a member of the K(+)-selective tandem-pore domain (K2P) channel family. Like many of the K2P channels, TASK1 is relatively insensitive to conventional channel blockers such as Ba(2+). In this paper we report the impact of mutating the pore-neighbouring histidine residues, which are involved in pH sensing, on the sensitivity to blockade by Ba(2+) and Cs(+); additionally we compare the selectivity of these channels to extracellular K(+), Na(+) and Rb(+). H98D and H98N mutants showed reduced selectivity for K(+) over both Na(+) and Rb(+), and significant permeation of Rb(+). This enhanced permeability must reflect changes in the structure or flexibility of the selectivity filter. Blockade by Ba(2+) and Cs(+) was voltage-dependent, indicating that both ions block within the pore. In 100 mm K(+), the K(D) at 0 mV for Ba(2+) was 36 +/- 10 mm (n = 6), whilst for Cs(+) it was 20 +/- 6.0 mm (n = 5). H98D was more sensitive to Ba(2+) than the wild-type (WT); in addition, the site at which Ba(2+) appears to bind was altered (WT: delta, 0.64 +/- 0.16, n = 6; H98D: delta, 0.16 +/- 0.03, n = 5, statistically different from WT; H98N: delta, 0.58 +/- 0.09, not statistically different from WT). Thus, the pore-neighbouring residue H98 contributes not only to the pH sensitivity of TASK1, but also to the structure of the conduction pathway.
authors.affiliation: School of Biomedical Sciences, Worsley Building, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Anthony D
authors.initials: AD
authors.lastname: O'Connell
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Morton
authors.forename: Asipu
authors.initials: A
authors.lastname: Sivaprasadarao
authors.forename: Malcolm
authors.initials: M
authors.lastname: Hunter
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: D009419:Nerve Tissue Proteins; D024683:Potassium Channels, Tandem Pore Domain; D011994:Recombinant Proteins; C420132:potassium channel subfamily K member 3; D002586:Cesium; D001464:Barium