Selectivity and interactions of Ba2+ and Cs+ with wild-type and mutant TASK1 K+ channels expressed in Xenopus oocytes

• Published in: The Journal of physiology 2005-02, Vol.562 (3), p.687-696
• Main Authors: O'Connell, Anthony D, Morton, Michael J, Sivaprasadarao, Asipu, Hunter, Malcolm
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution; Animals; Barium - pharmacology; Cell Membrane - drug effects; Cell Membrane - physiology; Cell Membrane Permeability - drug effects; Cells, Cultured; Cesium - pharmacology; Dose-Response Relationship, Drug; Electric Conductivity; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Membrane Potentials - drug effects; Membrane Potentials - physiology; Mice; Molecular and Genomic Physiology; Nerve Tissue Proteins - drug effects; Nerve Tissue Proteins - physiology; Oocytes - physiology; Potassium Channels, Tandem Pore Domain - drug effects; Potassium Channels, Tandem Pore Domain - physiology; Recombinant Proteins - metabolism; Reproducibility of Results; Sensitivity and Specificity; Structure-Activity Relationship; Xenopus laevis
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2004.079020

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.