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Molecular determinants of the inhibition of human Kv1.5 potassium currents by external protons and Zn 2+
Author(s) -
Kehl Steven J.,
Eduljee Cyrus,
Kwan Daniel C. H.,
Zhang Shetuan,
Fedida David
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.014456
Subject(s) - potassium , chemistry , potassium channel , isotopes of potassium , biophysics , biology , organic chemistry
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 m m K + o the p K 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 m m . 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.