Identification of Epoxyeicosatrienoic Acids as Endothelium-Derived Hyperpolarizing Factors

Abstract

Endothelial cells release several compounds, including prostacyclin, NO, and endothelium-derived hyperpolarizing factor (EDHF), that mediate the vascular effects of vasoactive hormones. The identity of EDHF remains unknown. Since arachidonic acid causes endothelium-dependent relaxations of coronary arteries through its metabolism to epoxyeicosatrienoic acids (EETs) by cytochrome P450, we wondered if the EETs represent EDHFs. Precontracted bovine coronary arteries relaxed in an endothelium-dependent manner to methacholine. The cytochrome P450 inhibitors, SKF 525A and miconazole, significantly attenuated these relaxations. They were also inhibited by tetraethylammonium (TEA),an inhibitor of Ca2+-activated K+ channels, and by high [K+]0 (20 mmol/L). Methacholine also caused hyperpolarization of coronary smooth muscle (-27 +/- 3.9 versus -40 +/- 5.1 mV), which was completely blocked by SKF 525A and miconazole. In vessels prelabeled with [3H] arachidonic acid, methacholine stimulated the release of 6-ketoprostaglandin F1alpha, 12-HETE, and the EETs. Arachidonic acid relaxed precontracted coronary arteries, which were also blocked by TEA, charybdotoxin, another Ca2+-activated K+ channel inhibitor, and high [K+]0. 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET relaxed precontracted coronary vessels (EC50, 1 X 10(-6) mol/L). The four regioisomers were equally active. TEA, charybdotoxin, and high [K+]0 attenuated the EET relaxations. 11,12-EET hyperpolarized coronary smooth muscle cells from -37 +/- 0.2 to -59 +/- 0.3 mV. In the cell-attached mode of patch clamp, both 14,15-EET and 11,12-EET increased the open-state probability of a Ca2+-activated K+ channel in coronary smooth muscle cells. This effect was blocked by TEA and charybdotoxin. These data support the hypothesis that the EETs are EDHFs.

Upregulation of endothelium-derived hyperpolarizing factor compensates for the loss of nitric oxide in mesenteric arteries of dahl salt-sensitive hypertensive rats

“…It has also been reported that EETs, another candidate for EDHF, 31 stimulate the transient receptor potential vanilloid type 4 channels, which increases the calcium influx, and subsequently activates BKCa channels in rat smooth muscle cells. 32 Taken together, it is plausible to speculate that enhanced EDHF-like relaxation in the mesenteric arteries of DS rats fed a high-salt diet could be attributable to an enhanced EETs/ transient receptor potential vanilloid type 4/BKCa signaling pathway.…”

Role of epoxyeicosatrienoic acids in protecting the myocardium following ischemia/reperfusion injury

“…For example, EETs activate Ca 2+ -sensitive K + channels (BK Ca ) in vascular smooth muscle cells resulting in hyperpolarization of the resting membrane potential and vasodilation of the coronary circulation [19][20][21]. This effect is diminished upon hydrolysis of EETs to DHETs by sEH [22].…”

Role of phospholipase C and diacylglyceride lipase pathway in arachidonic acid release and acetylcholine-induced vascular relaxation in rabbit aorta

“…The phospholipase inhibitors mepacrine and dimethyl-eicosadienoic acid (DEDA) decrease relaxation to ACh but not AA, suggesting AA or a metabolite may be involved in the relaxations (11). AA is metabolized by COX, lipoxygenase (LO), and cytochrome P-450 pathways into bioactive eicosanoids (10,30,40,48). Using specific inhibitors in rabbit aorta, Singer and Peach (51) first concluded that a LO metabolite mediates the NO-and PG-resistant relaxation to ACh (51).…”