An Inwardly Rectifying Potassium Channel in Apical Membrane of Calu-3 Cells

• Published in: The Journal of biological chemistry 2004-11, Vol.279 (45), p.46558-46565
• Main Authors: Wu, Jin V, Krouse, Mauri E, Rustagi, Arjun, Joo, Nam Soo, Wine, Jeffrey J
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - chemistry; Adenosine Triphosphate - metabolism; Barium - chemistry; Cell Line; Cell Membrane - metabolism; Cesium - chemistry; Chlorine - chemistry; Cystic Fibrosis Transmembrane Conductance Regulator - metabolism; Dose-Response Relationship, Drug; Electrophysiology; Humans; Hydrogen-Ion Concentration; Immediate-Early Proteins - metabolism; Kinetics; Kir5.1 Channel; Monomeric GTP-Binding Proteins - metabolism; Patch-Clamp Techniques; Potassium - chemistry; Potassium Channels - chemistry; Potassium Channels, Inwardly Rectifying - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - metabolism; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M406058200

Patch clamp methods and reverse transcription-polymerase chain reaction (RT-PCR) were used to characterize an apical K + channel in Calu-3 cells, a widely used model of human airway gland serous cells. In cell-attached and excised apical membrane patches, we found an inwardly rectifying K + channel (Kir). The permeability ratio was P Na / P K = 0.058. In 30 patches with both cystic fibrosis transmembrane conductance regulator and Kir present, we observed 79 cystic fibrosis transmembrane conductance regulator and 58 Kir channels. The average chord conductance was 24.4 ± 0.5 pS ( n = 11), between 0 and –200 mV, and was 9.6 ± 0.7 pS ( n = 8), between 0 and 50 mV; these magnitudes and their ratio of ∼2.5 are most similar to values for rectifying K + channels of the Kir4.x subfamilies. We attempted to amplify transcripts for Kir4.1, Kir4.2, and Kir5.1; of these only Kir4.2 was present in Calu-3 lysates. The channel was only weakly activated by ATP and was relatively insensitive to internal pH. External Cs + and Ba 2+ blocked the channel with K d values in the millimolar range. Quantitative modeling of Cl – secreting epithelia suggests that secretion rates will be highest and luminal K + will rise to 16–28 m m if 11–25% of the total cellular K + conductance is placed in the apical membrane (Cook, D. I., and Young, J. A. (1989) J. Membr. Biol. 110, 139–146). Thus, we hypothesize that the K + channel described here optimizes the rate of secretion and is involved in K + recycling for the recently proposed apical H + -K + -ATPase in Calu-3 cells.