Primary structure and functional expression of a cortical collecting duct Kir channel.
Maintenance of a negative membrane potential in the cortical collecting duct (CCD) principal cell depends on a small-conductance, inward-rectifying basolateral membrane K+ (Kir) channel. In the present study, a candidate cDNA encoding this K+ channel, CCD-IRK3, was isolated from a mouse collecting duct cell line, M1. CCD-IRK3 shares a high degree of homology with a human brain inward-rectifier K+ channel (Kir 2.3). By Northern analysis, CCD-IRK3 transcript (2.9 kb) was readily detected in M1 CCD cells but not in Madin-Darby canine kidney, LLC-PK1, Chinese hamster ovary, or monkey kidney fibroblast cell lines. CCD-IRK3-specific reverse transcription-polymerase chain reaction confirmed bonafide expression in the kidney. Functional expression studies in Xenopus oocytes revealed that CCD-IRK3 operates as strongly inward-rectifying K+ channel. The cation selectivity profile of CCD-IRK3 [ionic permeability values (PK/Pi), Tl > or = Rb > or = K+ >> NH4 > Na; inward-slope conductance (GK/Gi), Tl > or = K+ >> NH4 > Na > Rb] is similar to the macroscopic CCD basolateral membrane K+ conductance (GK/Gi, K+ >> NH4 > Rb; PK/Pi, Rb approximately equal to K+ >> NH4). CCD-IRK3 also exhibits the pharmacological features of the native channel. Patch-clamp analysis reveals that CCD-IRK3 functions as a high open probability, voltage-independent, small-conductance channel (14.5 pS), consistent with the native channel. Based on these independent lines of evidence, CCD-IRK3 is a possible candidate for the small-conductance basolateral Kir channel in the CCD.
Welling
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PA
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA.
D000595:Amino Acid Sequence; D000818:Animals; D000838:Anions / Q000378:metabolism; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D002414:Cations, Monovalent / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D006224:Cricetinae; D004285:Dogs; D004553:Electric Conductivity; D005260:Female; D000882:Haplorhini; D006801:Humans; D015640:Ion Channel Gating; D007668:Kidney; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D015221:Potassium Channels / Q000096:biosynthesis* / Q000737:chemistry* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014981:Xenopus
D000838:Anions; D002414:Cations, Monovalent; C099489:KCNJ4 protein, human; C490969:Kcnj4 protein, mouse; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins