Premium
Effect of Extracellular Cations on the Inward Rectifying K + Channels Kir2.1 and Kir3.1/Kir3.4
Author(s) -
Owen J. M.,
Quinn C. C.,
Leach R.,
Findlay J. B. C.,
Boyett M. R.
Publication year - 1999
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1111/j.1469-445x.1999.01806.x
Subject(s) - extracellular , chemistry , biophysics , xenopus , inward rectifier potassium ion channel , binding site , ion , analytical chemistry (journal) , ion channel , biochemistry , chromatography , biology , receptor , organic chemistry , gene
SUMMARY The effects of Ba 2+ , Mg 2+ , Ca 2+ and Na + as blocking ions were investigated in 90 and 10 mM extracellular K + solutions on the cloned inward rectifying K + channel Kir2.1 expressed in Xenopus oocytes. Some data were also obtained using another inward rectifying K + channel Kir3.1/Kir3.4. The addition of Ba 2+ caused a concentration‐, voltage‐ and time‐dependent block of both channels. Decreasing the extracellular K + concentration augmented the block. The data suggest that Ba 2+ blocks the channels by binding to a site within the channel pore and that the electrical binding distance, δ, of the site is significantly different for Kir2.1 and Kir3.1/Kir3.4 (∼ 0·38 and ∼ 0·22, respectively). Mg 2+ and Ca 2+ caused an instantaneous concentration‐ and voltage‐dependent block of both channels. With Kir2.1, decreasing the K + concentration augmented the block. The voltage dependence of the block was less than that of Ba 2+ (δ, ∼ 0·1), indicating a more superficial binding site for these ions within the channel pore. The affinity of the channels for Mg 2+ and Ca 2+ was ∼ 1000‐fold lower than that for Ba 2+ . Addition of Na + resulted in a concentration‐, voltage‐ and time‐dependent block of Kir2.1, similar to that observed with Ba 2+ . The competition between the blocking cations (for Kir2.1: Ba 2+ , Mg 2+ , Ca 2+ ; for Kir3.1/Kir3.4: Ba 2+ ) and extracellular K + suggests that the binding sites for the blocking cations may be sites to which K + binds as part of the normal passage of K + through the channels. It is possible that under normal physiological conditions naturally occurring extracellular cations may partly block the two inward rectifying K + channels.