title: Is the molecular composition of K(ATP) channels more complex than originally thought?
abstract: ATP-sensitive K+ (K(ATP)) channels are abundantly expressed in the heart and may be involved in the pathogenesis of myocardial ischemia. These channels are heteromultimeric, consisting of four pore-forming subunits (Kir6.1, Kir6.2) and four sulfonylurea receptor (SUR) subunits in an octameric assembly. Conventionally, the molecular composition of K(ATP) channels in cardiomyocytes and pancreatic beta -cells is thought to include the Kir6.2 subunit and either the SUR2A or SUR1 subunits, respectively. However, Kir6.1 mRNA is abundantly expressed in the heart, suggesting that Kir6.1 and Kir6.2 subunits may co-assemble to form functional heteromeric channel complexes. Here we provide two independent lines of evidence that heteromultimerization between Kir6.1 and Kir6.2 subunits is possible in the presence of SUR2A. We generated dominant negative Kir6 subunits by mutating the GFG residues in the channel pore to a series of alanine residues. The Kir6.1-AAA pore mutant subunit suppressed both wt-Kir6.1/SUR2A and wt-Kir6.2/SUR2A currents in transfected HEK293 cells. Similarly, the dominant negative action of Kir6.2-AAA does not discriminate between either of the wild-type subunits, suggesting an interaction between Kir6.1 and Kir6.2 subunits within the same channel complex. Biochemical data support this concept: immunoprecipitation with Kir6.1 antibodies also co-precipitates Kir6.2 subunits and conversely, immunoprecipitation with Kir6.2 antibodies co-precipitates Kir6.1 subunits. Collectively, our data provide direct electrophysiological and biochemical evidence for heteromultimeric assembly between Kir6.1 and Kir6.2. This paradigm has profound implications for understanding the properties of native K(ATP)channels in the heart and other tissues.
authors.affiliation: Department of Pediatric Cardiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Pountney
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Sun
authors.forename: L M
authors.initials: LM
authors.lastname: Porter
authors.forename: M N
authors.initials: MN
authors.lastname: Nitabach
authors.forename: T Y
authors.initials: TY
authors.lastname: Nakamura
authors.forename: D
authors.initials: D
authors.lastname: Holmes
authors.forename: E
authors.initials: E
authors.lastname: Rosner
authors.forename: M
authors.initials: M
authors.lastname: Kaneko
authors.forename: T
authors.initials: T
authors.lastname: Manaris
authors.forename: T C
authors.initials: TC
authors.lastname: Holmes
authors.forename: W A
authors.initials: WA
authors.lastname: Coetzee
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001578:Benzopyrans / Q000494:pharmacology; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D005822:Genetic Vectors; D005905:Glyburide / Q000494:pharmacology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000819:agonists / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D011233:Precipitin Tests; D021122:Protein Subunits; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D014162:Transfection
chemical_list: D000906:Antibodies; D001578:Benzopyrans; D004095:Dihydropyridines; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D012333:RNA, Messenger; C061050:bimakalim; D000255:Adenosine Triphosphate; D005905:Glyburide