INDEPENDENT TRAFFICKING OF K-ATP CHANNEL SUBUNITS TO THE PLASMA-MEMBRANE

K-ATP channels are unique in requiring two distinct subunits (Kir6.2, a potassium channel subunit) and SUR1 (an ABC protein) for generation of functional channels, To examine the cellular trafficking of K-ATP c hannel subunits, green fluorescent protein (GFP) was tagged to the cyt oplasmic N or C terminus of SUR1 and Kir6.2 subunits and to the C term inus of a dimeric fusion between SUR1 and Kir6.2 (SUR1-Kir6.2). AU tag ged constructs generated functional channels with essentially normal p roperties when coexpressed with the relevant other subunit. GFP-tagged Kir6.2 (Kir6.2-GFP) showed perinuclear and plasma membrane fluorescen ce patterns when expressed alone or with SUR1, and a very similar patt ern was observed when channel-forming SUR1-Kir6.2-GFP was expressed on its own. In contrast, whereas SUR1 (SUR1-GFP) also showed a perinucle ar and plasma membrane fluorescence pattern when expressed alone, an a pparently cytoplasmic fluorescence was observed when coexpressed with Kir6.2 subunits, The results indicate that Kir6.2 subunits traffic to the plasma membrane in the presence or absence of SUR1, in contradicti on to the hypothesis that homomeric Kir6.2 channels are not observed b ecause SUR1 is required as a chaperone to guide Kir6.2 subunits throug h the secretory pathway.