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1 Internal Medicine, Mayo Clinic, Rochester, Minnesota, USA
* To whom correspondence should be addressed. E-mail: Lee.honchi{at}mayo.edu.
Epoxyeicosatrienoic acids (EETs), the cytochrome P-450 epoxygenase metabolites of arachidonic acid, are candidates of endothelium-derived hyperpolarizing factors. We have previously reported that EETs are potent activators of the cardiac ATP-sensitive K+ (KATP) channels but their effects on the vascular KATP channels are unknown. Using whole-cell patch clamp techniques with 0.1 mM ATP in the pipette and holding at -60 mV, freshly isolated smooth muscle cells from rat mesenteric arteries had small glibenclamide-sensitive currents at baseline (13.1 ± 3.9 pA, n=5) that showed a 7.2-fold activation by 10 µM pinacidil (94.1 ± 21.9 pA/pF (n=7, p<0.05). 11,12-EET dose-dependently activated the KATP current with an apparent EC50 of 87 nM. Activation of the KATP channels by 500 nM 11,12-EET was inhibited by inclusion of the PKA inhibitor peptide (5 µM), but not by inclusion of the PKC inhibitor peptide (100 µM), in the pipette solution. These results were corroborated by vasoreactivity studies. 11,12-EET produced dose-dependent vasorelaxation in isolated small mesenteric arteries, and this effect was reduced by 50% with glibenclamide (10 µM) pre-incubation. The 11,12-EET effects on vasorelaxation were also significantly attenuated by pre-incubation with the cell-permeant myristoylated PKI(14-22); and in the presence of PKI, glibenclamide had no additional effects. These results suggest that 11,12-EET is a potent activator of the vascular KATP channels, and its effects are dependent on protein kinase A activities.
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