title: The selectivity, voltage-dependence and acid sensitivity of the tandem pore potassium channel TASK-1: contributions of the pore domains.
abstract: We have investigated the contribution to ionic selectivity of residues in the selectivity filter and pore helices of the P1 and P2 domains in the acid sensitive potassium channel TASK-1. We used site directed mutagenesis and electrophysiological studies, assisted by structural models built through computational methods. We have measured selectivity in channels expressed in Xenopus oocytes, using voltage clamp to measure shifts in reversal potential and current amplitudes when Rb+ or Na+ replaced extracellular K+. Both P1 and P2 contribute to selectivity, and most mutations, including mutation of residues in the triplets GYG and GFG in P1 and P2, made channels non-selective. We interpret the effects of these--and of other mutations--in terms of the way the pore is likely to be stabilised structurally. We show also that residues in the outer pore mouth contribute to selectivity in TASK-1. Mutations resulting in loss of selectivity (e.g. I94S, G95A) were associated with slowing of the response of channels to depolarisation. More important physiologically, pH sensitivity is also lost or altered by such mutations. Mutations that retained selectivity (e.g. I94L, I94V) also retained their response to acidification. It is likely that responses both to voltage and pH changes involve gating at the selectivity filter.
authors.affiliation: Molecular Physiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: K H
authors.initials: KH
authors.lastname: Yuill
authors.forename: P J
authors.initials: PJ
authors.lastname: Stansfeld
authors.forename: I
authors.initials: I
authors.lastname: Ashmole
authors.forename: M J
authors.initials: MJ
authors.lastname: Sutcliffe
authors.forename: P R
authors.initials: PR
authors.lastname: Stanfield
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004594:Electrophysiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D018408:Patch-Clamp Techniques; D018272:Porins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017434:Protein Structure, Tertiary; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000493:pharmacokinetics; D014162:Transfection; D014981:Xenopus
chemical_list: D009419:Nerve Tissue Proteins; D018272:Porins; D024683:Potassium Channels, Tandem Pore Domain; C420132:potassium channel subfamily K member 3; D012964:Sodium; D012413:Rubidium