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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS
1Institute for Medicine and Engineering and Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; 2Department of Medicine, Montreal Heart Institute, and University of Montreal, Montreal, Quebec, Canada; 3Department of Molecular, Cellular and Developmental Biology and Neuroscience Research Institute, University of California, Santa Barbara, California
Submitted 23 February 2005 ; accepted in final form 4 June 2005
Inward rectifier K+ channels (Kir) are a significant determinant of endothelial cell (EC) membrane potential, which plays an important role in endothelium-dependent vasodilatation. In the present study, several complementary strategies were applied to determine the Kir2 subunit composition of human aortic endothelial cells (HAECs). Expression levels of Kir2.1, Kir2.2, and Kir2.4 mRNA were similar, whereas Kir2.3 mRNA expression was significantly weaker. Western blot analysis showed clear Kir2.1 and Kir2.2 protein expression, but Kir2.3 protein was undetectable. Functional analysis of endothelial inward rectifier K+ current (IK) demonstrated that 1) IK current sensitivity to Ba2+ and pH were consistent with currents determined using Kir2.1 and Kir2.2 but not Kir2.3 and Kir2.4, and 2) unitary conductance distributions showed two prominent peaks corresponding to known unitary conductances of Kir2.1 and Kir2.2 channels with a ratio of 
4:6. When HAECs were transfected with dominant-negative (dn)Kir2.x mutants, endogenous current was reduced 50% by dnKir2.1 and 85% by dnKir2.2, whereas no significant effect was observed with dnKir2.3 or dnKir2.4. These studies suggest that Kir2.2 and Kir2.1 are primary determinants of endogenous K+ conductance in HAECs under resting conditions and that Kir2.2 provides the dominant conductance in these cells.
potassium channels; inward rectifier potassium channel
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