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Selectivity and interactions of Ba 2+ and Cs + with wild‐type and mutant TASK1 K + channels expressed in Xenopus oocytes
Author(s) -
O'Connell Anthony D.,
Morton Michael J.,
Sivaprasadarao Asipu,
Hunter Malcolm
Publication year - 2005
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.2004.079020
Subject(s) - chemistry , selectivity , mutant , wild type , biophysics , stereochemistry , analytical chemistry (journal) , biochemistry , biology , chromatography , catalysis , gene
The acid‐sensitive K + channel, TASK1 is a member of the K + ‐selective tandem‐pore domain (K2P) channel family. Like many of the K2P channels, TASK1 is relatively insensitive to conventional channel blockers such as Ba 2+ . In this paper we report the impact of mutating the pore‐neighbouring histidine residues, which are involved in pH sensing, on the sensitivity to blockade by Ba 2+ and Cs + ; additionally we compare the selectivity of these channels to extracellular K + , Na + and Rb + . H98D and H98N mutants showed reduced selectivity for K + over both Na + and Rb + , and significant permeation of Rb + . This enhanced permeability must reflect changes in the structure or flexibility of the selectivity filter. Blockade by Ba 2+ and Cs + was voltage‐dependent, indicating that both ions block within the pore. In 100 m m K + , the K D at 0 mV for Ba 2+ was 36 ± 10 m m ( n = 6) , whilst for Cs + it was 20 ± 6.0 m m ( n = 5) . H98D was more sensitive to Ba 2+ than the wild‐type (WT); in addition, the site at which Ba 2+ appears to bind was altered (WT: δ, 0.64 ± 0.16, n = 6; H98D: δ, 0.16 ± 0.03, n = 5, statistically different from WT; H98N: δ, 0.58 ± 0.09, not statistically different from WT). Thus, the pore‐neighbouring residue H98 contributes not only to the pH sensitivity of TASK1, but also to the structure of the conduction pathway.