Coimmunoprecipitation of Kir2.1 and Kir2.3 subunits. (A and B) Western blot analysis of membrane extracts from HEK293 cells transiently transfected with Kir2. 1, Kir2.3, or both, and of membrane extracts from isolated cardiomyocytes (CM). Note that the Kir2.1 protein of cardiomyocyte membranes migrated somewhat more slowly than that of transfected HEK293 cells. (C and D) Membrane extracts of HEK cells, transfected with Kir2.1, Kir2.3, or both, were precipitated with antibodies against Kir2.3 (C) or Kir2.1 (D) and subjected to Western blot analysis using antibodies against Kir2.1 (C) or Kir2.3 (D). IP, immunoprecipitation.