Evidence against functional heteromultimerization of the K-ATP channel subunits Kir6.1 and Kir6.2

K-ATP channels consist of pore-forming potassium inward rectifier (Kir6.x) subunits and sulfonylurea receptors (SURs), Although Kir6.1 or Kir6.2 coass emble with different SUR isoforms to form heteromultimeric functional K-ATP , channels, it is not known whether Kir6.1 and Kir6.2 coassemble with each other. To define the molecular identity of K-ATP channels, we used adenovir al gene transfer to express wild-type and dominant-negative coustructs of K ir6.1 and Kir6.2 in a heterologous expression system (A549 cells) and in na tive cells (rabbit ventricular myocytes), Dominant-negative (DN) Kir6.2 gen e transfer suppressed current through heterologously expressed SUR2A + Kir6 .2 channels. Conversely, DN Kir6.1 suppressed SUR2B + Kir6.1 current but ha d no effect on coexpressed SUR2A + Kir6.2, We next probed the ability of Ki r6.1 and Kir6.2 to affect endogenous K-ATP channels in adult rabbit ventric ular myocytes, using adenoviral vectors to achieve efficient gene transfer. Infection with the DN Kir6.2 virus for 72 h suppressed pinacidil-inducible K-ATP current density measured by whole-cell patch clamp. However, there w as no effect of infection with the DN Kir6.1 on the K-ATP current. Based on these functional assays, we conclude that Kir6.1 and Kir6.2 do not heterom ultimerize with each other and that Kir6.2 is the sole K-ATP pore-forming s ubunit in the surface membrane of heart cells.