IDENTIFICATION OF EPOXYEICOSATRIENOIC ACIDS AS ENDOTHELIUM-DERIVED HYPERPOLARIZING FACTORS

Endothelial cells release several compounds, including prostacyclin, N O, and endothelium-derived hyperpolarizing factor (EDHF), that mediate the vascular effects of vasoactive hormones. The identity of EDHF rem ains unknown. Since arachidonic acid causes endothelium-dependent rela xations of coronary arteries through its metabolism to epoxyeicosatrie noic acids (EETs) by cytochrome P-450 we wondered if the EETs represen t EDHFs. Precontracted bovine coronary arteries relaxed in an endothel ium-dependent manner to methacholine. The cytochrome P-450 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+](o) (20 mmol/L). Methachol ine also caused hyperpolarization of coronary smooth muscle (-27 +/- 3 .9 versus -40 +/- 5.1 mV), which was completely blocked by SKF 525A an d miconazole. In vessels prelabeled with [H-3]arachidonic acid: methac holine stimulated the release of 6-ketoprostaglandin F1(alpha), 12-HET E, and the EETs. Arachidonic acid relaxed precontracted coronary arter ies, which were also blocked by TEA, charybdotoxin, another Ca2+-activ ated K+ channel inhibitor, and high [K+](o). 14,15-EET, 11,12-EET, 8,9 -EET, and 5,6-EET relaxed precontracted coronary vessels (EC(50), 1x10 (-6) mol/L). The four regioisomers were equally active. TEA, charybdot oxin, and high [K+](o) attenuated the EET relaxations. 11,12-EET hyper polarized 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 11,1 2-EET increased the open-state probability of a Ca2+-activated K+ chan nel in coronary smooth muscle cells. This effect was blocked by TEA an d charybdotoxin. These data support the hypothesis that the EETs are E DHFs.