Epoxyeicosatrienoic Acids Are Released to Mediate Shear Stress–Dependent Hyperpolarization of Arteriolar Smooth Muscle

Abstract

Abstract-We hypothesized that shear stress stimulates the release of epoxyeicosatrienoic acids (EETs) from arteriolar endothelium, which directly hyperpolarize smooth muscle. To test this hypothesis, a perfusion system, consisting of two separate, serially connected chambers (A and B), was used. A donor vessel, isolated from gracilis muscle of female NO-deficient mice and rats, was cannulated in chamber A. In chamber B, an endothelium-denuded detector vessel isolated from mesentery of these animals was cannulated. In the presence of indomethacin, 5, 10, and 20 dyne/cm 2 shear stress elicited dilation of donor vessels, followed by dilation of detector vessels. Changes in membrane potential of the detector vessel smooth muscle cells in response to the perfusate from 5 and 10 dyne/cm 2 shear stress-stimulated donor vessels was also recorded (by ϷϪ12 to Ϫ15 and Ϫ20 to Ϫ30 mV, respectively). Exposing detector vessels to 30 mmol/L KCl or pretreating them with iberiotoxin abolished their hyperpolarization and dilation to the flow of perfusate. Pretreatment of donor vessels with PPOH, an inhibitor of cytochrome P-450/epoxygenase, eliminated dilator responses in both donor and detector vessels, as well as the hyperpolarization of detector vessels. GC-MS analysis showed increasing release of EETs into the perfusate collected from 1, 5, and 10 dyne/cm 2 shear stress-stimulated arterioles, which was abolished by PPOH. Thus, EETs, released from endothelial cells of donor vessels stimulated with shear stress, hyperpolarize smooth muscle of downstream detector vessels, confirming their identity as endotheliumderived hyperpolarizing factors and suggesting that gap junctional communication may not be necessary for shear stress-stimulated EDHF-mediated vasodilation. Key Words: NO deficiency Ⅲ shear stress Ⅲ EET Ⅲ hyperpolarization Ⅲ arterioles A lthough the chemical identity of endothelium-derived hyperpolarizing factor (EDHF) remains controversial, epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acids by cytochrome P450 (CYP)/epoxygenase, have been identified as a potential EDHF in a variety of vascular beds, including coronary, cerebral, renal, skeletal muscle vasculature, and human forearm and subcutaneous microvessels. 1 However, some studies that question the existence of EDHF suggest that electrical coupling of endothelial and smooth muscle cells through gap junctions mediates the activity. The idea that EDHF/EETs activate potassium channels in endothelial cells, leading to either the release of K ϩ , 2-4 or spread of current from endothelial cells, [5][6][7][8][9] to hyperpolarize smooth muscle, has attracted attention, because histological evidence of the existence of gap junctions between endothelial and smooth muscle cells and between endothelial cells was provided. 10,11 It was also reported that hyperpolarization of endothelial cells by injection of current or administration of ACh was conducted downstream to cause dilation of arterioles through endothelial gap junctions, 12,13 a response that was inhibit...

Action of epoxyeicosatrienoic acids on cellular function

“…Endothelial cells express CYP2C9 and CYP2J2 and are the main source of EETs in the vascular system (51,120,132). Bradykinin or methacholine increases endothelial EET production two-to fivefold (7,119), and shear stress also stimulates EET production by endothelial cells (76).…”

Endothelium-Derived Epoxyeicosatrienoic Acids and Vascular Function

“…This can undoubtedly occur when large amounts of EETs are generated, and EETs can be detected in the perfusate of isolated arteries after exposure to fluid shear stress 13 selective antagonist, 14,15-epoxyeicosa-5(Z)-monoenoic acid, is able to prevent the endothelium-dependent but NOand prostacyclin-independent relaxation of bovine coronary arteries in an elegant bioassay model. 15 EETs are not all metabolized via the same pathway, and although 5,6-EET is a preferred substrate for cyclooxygenase, 16 8,9-, 11,12-and 14,15-EET are metabolized to the corresponding dihydroxy derivatives (the dihydroxyeicosatrienoic acids) by the soluble epoxide hydrolase (sEH), 17 as well as by ␤-oxidation.…”

“…This can undoubtedly occur when large amounts of EETs are generated, and EETs can be detected in the perfusate of isolated arteries after exposure to fluid shear stress 13 or to agonist stimulation. 14 Moreover, a recently developed EET-selective antagonist, 14,15-epoxyeicosa-5(Z)-monoenoic acid, is able to prevent the endothelium-dependent but NOand prostacyclin-independent relaxation of bovine coronary arteries in an elegant bioassay model.…”

Contribution of epoxyeicosatrienoic acids to flow-induced dilation in arteries of male ERα knockout mice: role of aromatase

“…Experiments were conducted on arteries isolated from either gracilis muscle or mesentery because of the identical features of their flow-induced dilations, as well as the mediators responsible for the responses (10,11,13,14,36). The first-order gracilis muscle arteries were isolated for experiments of flow-induced dilation.…”

“…Second-order mesenteric arteries of the corresponding animals were used as detector vessels. The endothelium of the detector vessel was removed by injection of air into the vessel lumen as described previously (10,11). An RNA interference study was performed on second-order mesenteric arteries of ER␣-KO mice because they have adequate length with fewer branches.…”