Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and Na-K-Cl cotransporter NKCC1 isoform mediate the vasorelaxant action of genistein in isolated rat aorta

The soy phytoestrogen genistein is a potent vasorelaxant, but its mechanism of action is poorly understood. Here, we used endothelium-denuded rat aorta to investigate the role of the cyclic AMP(cAMP)-activated, cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel, and its associated Na-K-Cl cotransporter NKCCl. Isolated, endothelium-denuded rat aorta was contracted with phenylephrine 1 mu M, and the vasorelaxant responses to genistein were investigated under conditions where CFTR was inhibited by DPC (diphenylamine-2-carboxylic acid) or glibenclamide (n = 6 for compound). Both compounds fully antagonized the vasorelaxant responses to genistein, with IC50 = 57 +/- 18 mu M and 42 +/- 11 mu M for DPC and glibenclarnide respectively. H-89, a selective protein kinase A (PKA) inhibitor, blocked the vasorelaxant responses to genistem. Finally, the NKCCl inhibitor, bumetanide fully antagonized the vasorelaxant responses to genistein against phenylephrine- or KCl-induced contractions, with IC50 = 2.0 +/- 0.2 mu M and 1.6 +/- 0.5 mu M, respectively (n = 6 for condition). These results strongly suggest that CFTR opening is involved in the vasorelaxant action of genistein, and that cANW-dependent CFTR phosphorylation and chloride entry via the NKCCl cotransporter are required for genistein action. (c) 2006 Elsevier B.V. All rights reserved.