Enalapril Treatment Alters the Contribution of Epoxyeicosatrienoic Acids but Not Gap Junctions to Endothelium-Derived Hyperpolarizing Factor Activity in Mesenteric Arteries of Spontaneously Hypertensive Rats

Abstract

Reduction in endothelium-derived hyperpolarizing factor (EDHF)-mediated dilatory function in large, elastic arteries during hypertension is reversed after blood pressure normalization. We investigated whether similar mechanisms occurred in smaller mesenteric resistance arteries from aged Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHRs), and SHRs treated with the angiotensin-converting enzyme inhibitor, enalapril, using immunohistochemistry, serial-section electron microscopy, electrophysiology and wire myography. Unlike the superior mesenteric artery, EDHF relaxations in muscular mesenteric arteries were not reduced in SHRs, although morphological differences were found in the endothelium and smooth muscle. In WKY rats, SHRs and enalapril-treated SHRs, relaxations were mediated by small-, large-, and intermediate-conductance calcium-activated potassium channels, which were distributed in the endothelium, smooth muscle, and both layers, respectively. However, only WKY hyperpolarizations and relaxations were sensitive to gap junction blockers, and these arteries expressed more endothelial and myoendothelial gap junctions than arteries from SHRs. Responses in WKY rats, but not SHRs, were also reduced by inhibitors of epoxyeicosatrienoic acids (EETs), 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) and miconazole, although sensitivity to EET regioisomers was endothelium-independent in all rats. Enalapril treatment of SHRs reduced blood pressure and restored sensitivity to 14,15-EEZE, but not to gap junction blockers, and failed to reverse the morphological changes. In conclusion, the mechanisms underlying EDHF in muscular mesenteric arteries differ between WKY rats and SHRs, with gap junctions and EETs involved only in WKY rats. However, reduction of blood pressure in SHRs with enalapril restored a role for EETs, but not gap junctions, without reversing morphological changes, suggesting a differential control of chemical and structural alterations.The endothelium of arteries plays a critical role in the regulation of vascular tone by activating vasodilator pathways, the principal mediators being nitric oxide, prostaglandins, and endothelium-derived hyperpolarizing factor (EDHF). The action of EDHF depends on hyperpolarization and relaxation of smooth muscle cells that is initiated in the endothelium, with a rise in intracellular calcium, activation of small-conductance (SK Ca ) and intermediate-conductance (IK Ca ) calcium-dependent potassium channels, and hyperpolarization of the endothelial membrane. Although the mechanism by which endothelial hyperpolarization is transduced to smooth muscle hyperpolarization is still controversial and may vary among different vascular beds and species, there is developing consen-

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

“…9,10 We have previously shown that EDHF-mediated hyperpolarization and relaxation were decreased in the superior mesenteric arteries of 12-month-old spontaneously hypertensive rats (SHR) compared with age-matched normotensive Wistar-Kyoto rats and that the impairment of the EDHF pathway accounted, at least in part, for the endothelial dysfunction in this model. 11 Several mechanisms have been proposed to explain the reduced EDHF-mediated responses in mesenteric arteries of SHR: change in the expression profile of gap junctions, [12][13][14] increased activity of calcium-activated chloride channels 15 and reduced expression of small conductance calciumdependent potassium channels. 16 In contrast, Sofola et al 17 have reported that EDHF-like relaxation is upregulated in the mesenteric arteries of Sprague-Dawley rats fed a high-salt diet to compensate for the loss of NO.…”

Regulation of Cellular Communication by Signaling Microdomains in the Blood Vessel Wall

“…With the development of gap junction mimetic peptides such as [37][38][39][40][41][42][43] Gap 27, 40 Gap27, [37][38][39][40] Gap26, and 43 Gap26, the role of specific connexin isoforms was initially thought to be further clarified. Several reports demonstrated an inhibitory effect of these connexinmimetic peptides on indomethacin-and L-NAMEresistant relaxation to acetylcholine (Chaytor et al, 1998(Chaytor et al, , 2003(Chaytor et al, , 2005Dora et al, 1999;Sandow et al, 2002;Ellis et al, 2009). It is noteworthy that the [37][38][39][40][41][42][43] Gap 27, 40 Gap27, and [37][38][39][40] Gap26 were shown to inhibit VSMCs hyperpolarization upon acetylcholine stimulation, whereas they had no effect on the hyperpolarization of ECs (Sandow et al, 2002;Chaytor et al, 2003Chaytor et al, , 2005Ellis et al, 2009).…”

“…Several reports demonstrated an inhibitory effect of these connexinmimetic peptides on indomethacin-and L-NAMEresistant relaxation to acetylcholine (Chaytor et al, 1998(Chaytor et al, , 2003(Chaytor et al, , 2005Dora et al, 1999;Sandow et al, 2002;Ellis et al, 2009). It is noteworthy that the [37][38][39][40][41][42][43] Gap 27, 40 Gap27, and [37][38][39][40] Gap26 were shown to inhibit VSMCs hyperpolarization upon acetylcholine stimulation, whereas they had no effect on the hyperpolarization of ECs (Sandow et al, 2002;Chaytor et al, 2003Chaytor et al, , 2005Ellis et al, 2009). In contrast, the use of 43 Gap 26,40 Gap 27, and 37,43 Gap 27 in a different study failed to inhibit the EDH-mediated response, which is in line with other studies that have now called into Regulation of Cellular Communication in Blood Vessel Wall question the specificity of the connexin mimetics [e.g., Table 4 (Mather et al, 2005;Dahl, 2007;Wang et al, 2007)].…”

Downregulation of Endothelial Transient Receptor Potential Vanilloid Type 4 Channel and Small-Conductance of Ca 2+ -Activated K + Channels Underpins Impaired Endothelium-Dependent Hyperpolarization in Hypertension

“…Mesenteric arteries (20 , and anti-β-actin (AC-15; Sigma-Aldrich, St. Louis, MO) antibodies (1:1000 in Can Get Signal Solution 1; Toyobo, Osaka, Japan), for isolated vessels. Blots were then washed with phosphatebuffered saline with Tween 20 before the addition of goat anti-rabbit or goat antimouse secondary antibodies (1:10 000 in Can Get Signal solution 2; Toyobo) for 1 hour at room temperature.…”

“…9 However, previous studies did not observe a positive correlation between EDH-mediated responses and the number of MEGJs in arteries of SHR. 19,20 Thus, the underlying mechanisms of the impaired EDHmediated responses during hypertension remain to be clarified. Because the Ca 2+ influx through endothelial TRPV4 and the subsequent activation of SK Ca /IK Ca seems to be involved in EDH-mediated responses in rat mesenteric arteries, 13 we speculated that an impairment of endothelial TRPV4 and SK Ca / IK Ca could underpin the impaired EDH-mediated responses in mesenteric arteries of genetically hypertensive rats.…”