Is the molecular composition of K-ATP channels more complex than originally thought?

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, Ki r6.2) and four sulfonylurea receptor (SUR) subunits in an octameric assembl y. Conventionally, the molecular composition of K-ATP channels in cardiomyo cytes and pancreatic beta -cells is thought to include the Kir6.2 subunit a nd either the SUR2A or SUR1 subunits, respectively. However, Kir6.1 mRNA is abundantly expressed in the heart, suggesting that Kir6.1 and Kir6.2 subun its may co-assemble to form functional heteromeric channel complexes. Here we provide two independent lines of evidence that heteromultimerization bet ween Kir6.1 and Kir6.2 subunits is possible in the presence of SUR2A, We ge nerated 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 s ubunit suppressed both wt-Kir6.1/SUR2A and wt-Kir6.2/SUR2A currents in tran sfected 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 K ir6.1 antibodies also co-precipitates Kir6.2 subunits and conversely immuno precipitation with Kir6.2 antibodies co-precipitates Kir6.1 subunits. Colle ctively our data provide direct electrophysiological and biochemical eviden ce for heteromultimeric assembly between Kir6.1 and Kir6.2, This paradigm h as profound implications for understanding the properties of native K-ATP c hannels in the heart and other tissues. (C) 2001 Academic Press.