A mechanism for ATP-sensitive potassium channel diversity: Functional coassembly of two pore-forming subunits.
ATP-sensitive potassium channels are an octomeric complex of four pore-forming subunits of the Kir 6.0 family and four sulfonylurea receptors. The Kir 6.0 family consists of two known members, Kir 6.1 and Kir 6.2, with distinct functional properties. The tetrameric structure of the pore-forming domain leads to the possibility that mixed heteromultimers may form. In this study, we examine this by using biochemical and electrophysiological techniques after heterologous expression of these subunits in HEK293 cells. After the coexpression of Kir 6.1 and Kir 6.2, Kir 6.1 can be coimmunoprecipitated with isoform-specific Kir 6.2 antisera and vice versa. Coexpression of SUR2B and Kir 6.2 with Kir 6.1 dominant negatives at a 1:1 expression ratio and vice versa led to a potent suppression of current. Kir 6.1, and Kir 6.2 dominant negative mutants were without effect on an inwardly rectifying potassium channel from a different family, Kir 2.1. Single-channel analysis, after coexpression of SUR2B, Kir 6.1, and Kir 6.2, revealed the existence of five distinct populations with differing single-channel current amplitudes. All channel populations were inhibited by glibenclamide. A dimeric Kir 6.1-Kir 6.2 construct expressed with SUR2B had a single-channel conductance intermediate between that of either Kir 6.2 or Kir 6.1 expressed with SUR2B. In conclusion, Kir 6.1 and Kir 6.2 readily coassemble to produce functional channels, and such phenomena may contribute to the diversity of nucleotide-regulated potassium currents seen in native tissues.
Cui
Y
Y
Centre for Clinical Pharmacology, Department of Medicine, University College London, The Rayne Institute, 5 University Street, London WC1E 6JJ, United Kingdom.
Giblin
J P
JP
Clapp
L H
LH
Tinker
A
A
D018528:ATP-Binding Cassette Transporters; D000200:Action Potentials; D000595:Amino Acid Sequence; D000818:Animals; D001704:Biopolymers; D002460:Cell Line; D005905:Glyburide / Q000494:pharmacology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D007668:Kidney / Q000166:cytology; D046911:Macromolecular Substances; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000276:immunology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D055503:Protein Multimerization; D021122:Protein Subunits; D011817:Rabbits; D011955:Receptors, Drug / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013329:Structure-Activity Relationship; D064233:Sulfonylurea Receptors; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; D001704:Biopolymers; D046911:Macromolecular Substances; D010446:Peptide Fragments; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms; D021122:Protein Subunits; D011955:Receptors, Drug; D011993:Recombinant Fusion Proteins; D064233:Sulfonylurea Receptors; D011188:Potassium; D005905:Glyburide