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1Department of Clinical and Experimental Medicine, Clinica Medica 5, University of Padova, Padova, Italy; and 2Department of Pharmacology, New York Medical College, Valhalla, New York
Submitted 19 January 2006 ; accepted in final form 30 May 2006
11,12-Epoxyeicosatrienoic acid (11,12-EET), a potent vasodilator produced by the endothelium, acts on calcium-activated potassium channels and shares biological activities with the heme oxygenase/carbon monoxide (HO/CO) system. We examined whether activation of HO mediates the dilator action of 11,12-EET, and that of the other EETs, on rat mesenteric arteries. Dose-response curves (109 to 106 M) to 5,6-EET, 8,9-EET, 11,12-EET, 14,15-EET, and ACh (109 to 104 M) were evaluated in preconstricted (106 mol/l phenylephrine) mesenteric arteries (<350 µm diameter) in the presence or absence of 1) the cyclooxygenase inhibitor indomethacin (2.8 µM), 2) the HO inhibitor chromium mesoporphyrin (CrMP) (15 µM), 3) the soluble guanylyl cyclase (GC) inhibitor ODQ (10 µM), and 4) the calcium-activated potassium channel inhibitor iberiotoxin (25 nM). The vasodilator response to 11,12-EET was abolished by CrMP and iberiotoxin, whereas indomethacin and ODQ had no effect. In contrast, the effect of ACh was attenuated by ODQ but not by CrMP. The vasodilator effect of 8,9-EET, like that of 11,12-EET, was greatly attenuated by HO inhibition. In contrast, the mesenteric vasodilator response to 5,6-EET was independent of both HO and GC, whereas that to 14,15-EET demonstrated two components, an HO and a GC, of equal magnitude. Incubation of mesenteric microvessels with 11,12-EET caused a 30% increase in CO release, an effect abolished by inhibition of HO. We conclude that the rat mesenteric vasodilator action of 11,12-EET is mediated via an increase in HO activity and an activation of calcium-activated potassium channels.
epoxygenase; carbon monoxide; endothelial cell; mesenteric artery
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