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External K + relieves the block but not the gating shift caused by Zn 2+ in human Kv1.5 potassium channels
Author(s) -
Zhang Shetuan,
Kwan Daniel C. H.,
Fedida David,
Kehl Steven J.
Publication year - 2001
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 - 10.1111/j.1469-7793.2001.0349f.x
Subject(s) - gating , chemistry , conductance , potassium , block (permutation group theory) , allosteric regulation , analytical chemistry (journal) , potassium channel , extracellular , biophysics , nuclear magnetic resonance , physics , biochemistry , enzyme , chromatography , condensed matter physics , geometry , mathematics , organic chemistry , biology
1 We used the whole‐cell recording technique to examine the effect of extracellular Zn 2+ on macroscopic currents due to Kv1.5 channels expressed in the human embryonic kidney cell line HEK293. 2 Fits of a Boltzmann function to tail current amplitudes showed that 1 m m Zn 2+ shifted the half‐activation voltage from ‐10.2 ± 0.4 to 21.1 ± 0.7 mV and the slope factor increased from 6.8 ± 0.4 to 9.4 ± 0.7 mV. The maximum conductance in 1 m m Zn 2+ and with 3.5 m m K + o was 33 ± 7 % of the control value. 3 In physiological saline the apparent K D for the Zn 2+ block was 650 ± 24 μ m and was voltage independent. A Hill coefficient of 1.0 ± 0.03 implied that block is mediated by the occupation of a single binding site. 4 Increasing the external concentration of K + ([K + ] o ) inhibited the block by Zn 2+ . Estimates of the apparent K D of the Zn 2+ block in 0, 5 and 135 m m K + were 69, 650 and 2100 μ m , respectively. External Cs + relieved the Zn 2+ block but was less effective than K + . Changing [K + ] o did not affect the Zn 2+ ‐induced gating shift. 5 A model of allosteric inhibition fitted to the relationship between the block by Zn 2+ and the block relief by external K + gave K D estimates of ≈70 μ m for Zn 2+ and ≈500 μ m for K + . 6 We propose that the gating shift and the block caused by Zn 2+ are mediated by two distinct sites and that the blocking site is located in the external mouth of the pore.