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Expression and permeation properties of the K + channel Kir7.1 in the retinal pigment epithelium
Author(s) -
Shimura Masahiko,
Yuan Yukun,
Chang Jinghua T.,
Zhang Suiyuan,
Campochiaro Peter A.,
Zack Donald J.,
Hughes Bret A.
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.1469-7793.2001.0329i.x
Subject(s) - retinal pigment epithelium , conductance , chemistry , patch clamp , biophysics , potassium channel , microbiology and biotechnology , extracellular , analytical chemistry (journal) , biology , retinal , biochemistry , chromatography , physics , receptor , condensed matter physics
1 Bovine Kir7.1 clones were obtained from a retinal pigment epithelium (RPE)‐subtracted cDNA library. Human RPE cDNA library screening resulted in clones encoding full‐length human Kir7.1 . 2 Northern blot analysis indicated that bovine Kir7.1 is highly expressed in the RPE. 3 Human Kir7.1 channels were expressed in Xenopus oocytes and studied using the two‐electrode voltage‐clamp technique. 4 The macroscopic Kir7.1 conductance exhibited mild inward rectification and an inverse dependence on extracellular K + concentration ([K + ] o ). The selectivity sequence based on permeability ratios was K + (1.0) ≈ Rb + (0.89) > Cs + (0.013) > Na + (0.003) ≈ Li + (0.001) and the sequence based on conductance ratios was Rb + (9.5) >> K + (1.0) > Na + (0.458) > Cs + (0.331) > Li + (0.139). 5 Non‐stationary noise analysis of Rb + currents in cell‐attached patches yielded a unitary conductance for Kir7.1 of ≈2 pS. 6 In whole‐cell recordings from freshly isolated bovine RPE cells, the predominant current was a mild inwardly rectifying K + current that exhibited an inverse dependence of conductance on [K + ] o . The selectivity sequence based on permeability ratios was K + (1.0) ≈ Rb + (0.89) > Cs + (0.021) > Na + (0.003) ≈ Li + (0.002) and the sequence based on conductance ratios was Rb + (8.9) >> K + (1.0) > Na + (0.59) > Cs + (0.23) > Li + (0.08). 7 In cell‐attached recordings with Rb + in the pipette, inwardly rectifying currents were observed in nine of 12 patches of RPE apical membrane but in only one of 13 basolateral membrane patches. 8 Non‐stationary noise analysis of Rb + currents in cell‐attached apical membrane patches yielded a unitary conductance for RPE Kir of ≈2 pS. 9 On the basis of this molecular and electrophysiological evidence, we conclude that Kir7.1 channel subunits comprise the K + conductance of the RPE apical membrane.