Constitutive inactivation of the hKv1.5 mutant channel, H463G, in K+-free solutions at physiological pH.
Extracellular acidification and reduction of extracellular K(+) are known to decrease the currents of some voltage-gated potassium channels. Although the macroscopic conductance of WT hKv1.5 channels is not very sensitive to [K(+)](o) at pH 7.4, it is very sensitive to [K(+)](o) at pH 6.4, and in the mutant, H463G, the removal of K(+)(o) virtually eliminates the current at pH 7.4. We investigated the mechanism of current regulation by K(+)(o) in the Kv1.5 H463G mutant channel at pH 7.4 and the wild-type channel at pH 6.4 by taking advantage of Na(+) permeation through inactivated channels. Although the H463G currents were abolished in zero [K(+)](o), robust Na(+) tail currents through inactivated channels were observed. The appearance of H463G Na(+) currents with a slow rising phase on repolarization after a very brief depolarization (2 ms) suggests that channels could activate directly from closed-inactivated states. In wild-type channels, when intracellular K(+) was replaced by NMG(+) and the inward Na(+) current was recorded, addition of 1 mM K(+) prevented inactivation, but changing pH from 7.4 to 6.4 reversed this action. The data support the idea that C-type inactivation mediated at R487 in Kv1.5 channels is influenced by H463 in the outer pore. We conclude that both acidification and reduction of [K(+)](o) inhibit Kv1.5 channels through a common mechanism (i.e., by increasing channel inactivation, which occurs in the resting state or develops very rapidly after activation).
Zhang
Shetuan
S
Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, University of Manitoba, Winnipeg, Canada.
Eduljee
Cyrus
C
Kwan
Daniel C H
DC
Kehl
Steven J
SJ
Fedida
David
D
D001826:Body Fluids / Q000737:chemistry*; D002478:Cells, Cultured; D045604:Extracellular Fluid / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000502:physiology*; D007668:Kidney / Q000737:chemistry / Q000378:metabolism*; D051666:Kv1.5 Potassium Channel; D008564:Membrane Potentials / Q000502:physiology; D009154:Mutation; D011188:Potassium / Q000737:chemistry* / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry* / Q000502:physiology*; D013329:Structure-Activity Relationship
C496981:KCNA5 protein, human; D051666:Kv1.5 Potassium Channel; D024642:Potassium Channels, Voltage-Gated; D011188:Potassium