title: Molecular determinants of the inhibition of human Kv1.5 potassium currents by external protons and Zn(2+).
abstract: Using human Kv1.5 channels expressed in HEK293 cells we assessed the ability of H+o to mimic the previously reported action of Zn(2+) to inhibit macroscopic hKv1.5 currents, and using site-directed mutagenesis, we addressed the mechanistic basis for the inhibitory effects of H(+)(o) and Zn(2+). As with Zn(2+), H(+)(o) caused a concentration-dependent, K(+)(o)-sensitive and reversible reduction of the maximum conductance (g(max)). With zero, 5 and 140 mM K(+)(o) the pK(H) for this decrease of g(max) was 6.8, 6.2 and 6.0, respectively. The concentration dependence of the block relief caused by increasing [K(+)](o) was well fitted by a non-competitive interaction between H(+)(o) and K(+)(o), for which the K(D) for the K(+) binding site was 0.5-1.0 mM. Additionally, gating current analysis in the non-conducting mutant hKv1.5 W472F showed that changing from pH 7.4 to pH 5.4 did not affect Q(max) and that charge immobilization, presumed to be due to C-type inactivation, was preserved at pH 5.4. Inhibition of hKv1.5 currents by H+o or Zn(2+) was substantially reduced by a mutation either in the channel turret (H463Q) or near the pore mouth (R487V). In light of the requirement for R487, the homologue of Shaker T449, as well as the block-relieving action of K(+)(o), we propose that H(+) or Zn(2+) binding to histidine residues in the pore turret stabilizes a channel conformation that is most likely an inactivated state.
authors.affiliation: Department of Physiology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia, Canada V6T 1Z3. skehl@interchange.ubc.ca
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Kehl
authors.forename: Cyrus
authors.initials: C
authors.lastname: Eduljee
authors.forename: Daniel C H
authors.initials: DC
authors.lastname: Kwan
authors.forename: Shetuan
authors.initials: S
authors.lastname: Zhang
authors.forename: David
authors.initials: D
authors.lastname: Fedida
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D001667:Binding, Competitive / Q000187:drug effects; D002586:Cesium / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism / Q000502:physiology; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D007700:Kinetics; D051666:Kv1.5 Potassium Channel; D008564:Membrane Potentials / Q000502:physiology; D009154:Mutation / Q000235:genetics / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated; D011522:Protons; D015032:Zinc / Q000494:pharmacology*
chemical_list: C496981:KCNA5 protein, human; D051666:Kv1.5 Potassium Channel; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011522:Protons; D002586:Cesium; D015032:Zinc; D011188:Potassium