6533b861fe1ef96bd12c4481

RESEARCH PRODUCT

NADPH Oxidase Accounts for Enhanced Superoxide Production and Impaired Endothelium-Dependent Smooth Muscle Relaxation in BKβ1 −/− Mice

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Objective— Nitric oxide (NO)-induced vasorelaxation involves activation of large conductance Ca 2+ -activated K + channels (BK). A regulatory BKβ1 subunit confers Ca 2+ , voltage, and NO/cGMP sensitivity to the BK channel. We investigated whether endothelial function and NO/cGMP signaling is affected by a deletion of the β1-subunit. Methods and Results— Vascular superoxide in BKβ1 −/− was measured using the fluorescent dye hydroethidine and lucigenin-enhanced chemiluminescence. Vascular NO formation was analyzed using electron paramagnetic resonance (EPR), expression of NADPH oxidase subunits, the endothelial NO synthase (eNOS), the soluble guanylyl cyclase (sGC), as well as the activity and expression of the cyclic GMP-dependent kinase I (cGK-I) were assessed by Western blotting technique. eNOS, sGC, cGK-I expression and acetylcholine-induced NO production were unaltered in Bkβ1 −/− animals, whereas endothelial function was impaired and the activity of the cGK-I was reduced. Vascular O 2 − and expression of the NADPH oxidase subunits p67 phox and Nox1 were increased. Endothelial dysfunction was normalized by the NADPH oxidase inhibitor apocynin. Potassium chloride- and iberiotoxin-induced depolarization mimicked the effect of BKβ1-deletion by increasing vascular O 2 − in an NADPH-dependent fashion. Conclusions— The deletion of BKβ1 causes endothelial dysfunction by increasing O 2 − formation via increasing activity and expression of the vascular NADPH oxidase.