Molecular composition of mitochondrial ATP-sensitive potassium channels probed by viral Kir gene transfer

Heart cells contain ATP-sensitive potassium (K-APT) channels in both the sa rcolemma and the inner mitochondrial membrane. The sarcolemmal channels are believed to be heteromultimeric complexes of sulfonylurea receptors (SUR) and potassium inward rectifier (Kir) gene products, but the molecular ident ity of mitochondrial K-ATP (mitoK(ATP)) channels remains unclear. To probe the molecular composition of It, channels, we used adenoviral gene transfer to express wild-type (WT) and dominant-negative (AFA) constructs of Kir6.1 and 6.2 in rabbit ventricular myocytes. None of the Kir6.1 or 6.2 construc ts affected mitoK(ATP) channel activity as assayed by confocal imaging of f lavoprotein fluorescence, contradicting the proposal, based on subcellular antibody localization, that Kir6.1 forms part of mitoK(ATP) channels. As pr eviously reported, dominant-negative Kir6.2 gene transfer suppressed sarcol emmal K-ATP current, while Kir6.1 constructs had no effect on sarcolemmal a ctivity. Immunohistochemistry with an anti-Kir6.1 antibody revealed express ion of this protein in heart but no apparent co-localization with mitochond ria. Thus, the available evidence indicates that both Kir6.1 and 6.2 are ex pressed in ventricular myocytes, but neither plays a discernible functional role in the mitoK(ATP) channel. (C) 2000 Academic Press.