An inwardly rectifying potassium channel in apical membrane of Calu-3 cells.
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 PNa/PK = 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 approximately 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 Ba2+ blocked the channel with Kd 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 mm 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.
Cystic Fibrosis Research Laboratory, Stanford University, Stanford, California 94305-2130, USA.
Jin V
JV
Wu
Mauri E
ME
Krouse
Arjun
A
Rustagi
Nam Soo
NS
Joo
Jeffrey J
JJ
Wine
D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D001464:Barium / Q000737:chemistry; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002586:Cesium / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017874:Immediate-Early Proteins / Q000378:metabolism; D007700:Kinetics; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000737:chemistry; D015221:Potassium Channels / Q000737:chemistry*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D000097062:Kir5.1 Channel; D000098854:Kcnj10 Channel
D000255:Adenosine Triphosphate; D001464:Barium; D002586:Cesium; D002713:Chlorine; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D017874:Immediate-Early Proteins; D020559:Monomeric GTP-Binding Proteins; D011188:Potassium; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D000097062:Kir5.1 Channel; D000098854:Kcnj10 Channel; C505032:CFTR protein, human; C489469:Kir4.2 channel; C490245:GEM protein, human