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1 Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA, USA
2 Department of Medicine, University of Montreal, Montreal, Canada
3 Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, USA
* To whom correspondence should be addressed. E-mail: ilevitan{at}mail.med.upenn.edu.
Inwardly-rectifying K+ (Kir) channels are a significant determinant of endothelial-cell membrane potential, which plays an important role in endothelium-dependent vasodilatation. Several complementary strategies were applied to determine the Kir2-subunit composition of human aortic endothelial cells (HAECs). Expression levels of Kir2.1, 2.2 and 2.4 mRNAs 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 inwardly-rectifying K+ current demonstrated that: (i) inwardly-rectifying K+ current sensitivity to Ba2+ and pH were consistent with currents determined by Kir2.1 and Kir2.2 but not Kir2.3 and Kir2.4, and (ii) unitary- conductance distributions showed two prominent peaks corresponding to known unitary conductances of Kir2.1 and Kir2.2 channels with a ratio of approximately 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 is the dominant conductance in these cells.
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