Role of superoxide and angiotensin II suppression in salt-induced changes in endothelial Ca²⁺ signaling and NO production in rat aorta

Abstract

Male Sprague-Dawley rats were maintained on a low-salt (LS) diet (0.4% NaCl) or changed to a high-salt (HS) diet (4% NaCl) for 3 days. Increases in intracellular Ca 2ϩ ([Ca 2ϩ ]i) in response to methacholine (10 M) and histamine (10 M) were significantly attenuated in aortic endothelial cells from rats fed a HS diet, whereas thapsigargin (10 M)-induced increases in [Ca 2ϩ ]i were unaffected. Methacholineinduced nitric oxide (NO) production was eliminated in endothelial cells of aortas from rats fed a HS diet. Low-dose ANG II infusion (5 ng ⅐ kg Ϫ1 ⅐ min Ϫ1 iv) for 3 days prevented impaired [Ca 2ϩ ]i signaling response to methacholine and histamine and restored methacholineinduced NO production in aortas from rats on a HS diet. Adding Tempol (500 M) to the tissue bath to scavenge superoxide anions increased NO release and caused N -nitro-L-arginine methyl estersensitive vascular relaxation in aortas from rats fed a HS diet but had no effect on methacholine-induced Ca 2ϩ responses. Chronic treatment with Tempol (1 mM) in the drinking water restored NO release, augmented vessel relaxation, and increased methacholine-induced Ca 2ϩ responses significantly in aortas from rats on a HS diet but not in aortas from rats on a LS diet. These findings suggest that 1) agonist-induced Ca 2ϩ responses and NO levels are reduced in aortas of rats on a HS diet; 2) increased vascular superoxide levels contribute to NO destruction, and, eventually, to impaired Ca 2ϩ signaling in the vascular endothelial cells; and 3) reduced circulating ANG II levels during elevated dietary salt lead to elevated superoxide levels, impaired endothelial Ca 2ϩ signaling, and reduced NO production in the endothelium. endothelium; sodium; dietary salt intake; vascular relaxation; nitric oxide A VARIETY OF AGENTS, including muscarinic agonists such as ACh, dilate blood vessels by stimulating the synthesis of nitric oxide (NO) by endothelial NO synthase. Endothelial cell activation in response to agonists and autacoids leads to NO formation via receptor-mediated increases in intracellular calcium ion concentration ([Ca 2ϩ ] i ). However, emerging evidence indicates that endothelial NO synthase activity can be affected by a variety of other mechanisms that are independent of [Ca 2ϩ ] i (7,12,21,26,27). This raises the possibility that changes in NO production under some physiological conditions may be independent of changes in endothelial [Ca 2ϩ ] i . Endothelium-dependent relaxation in response to ACh is impaired in the aorta, resistance arteries, and microvessels of rats fed a high-salt (HS) diet (2-5, 15, 16, 18, 28). Elevated dietary salt intake causes suppression of plasma ANG II levels (8, 9), and previous studies (18,30,31) have demonstrated that the impaired vascular relaxation in Sprague-Dawley rats fed a HS diet can be prevented by a continuous intravenous infusion of a low dose of ANG II to maintain normal circulating levels of ANG II.In the present study, we tested the hypothesis that receptormediated increases in [Ca 2ϩ ] i and/or...

Critical Role of Lipid Raft Redox Signaling Platforms in Endostatin-Induced Coronary Endothelial Dysfunction

“…Increased O 2 .Ϫ could reduce the bioavailability of NO, resulting in impairment of endothelium-dependent vasodilation, as shown in our previous studies and by others. 4,[41][42][43][44] In summary, the present study demonstrated that EST is able to induce endothelial dysfunction as an early-stage acute action, which is associated with assembling and activation of NADPH oxidase in LR clusters. The clustered LRs together with activated NADPH oxidase constitute a redox signaling platform mediating the pathological actions of EST on the vascular endothelium.…”

Mutation of Plekha7 attenuates salt-sensitive hypertension in the rat

“…The increased influx of Ca 2+ in mutant vessels coincided with elevated NO bioavailability ( Fig. 6 A and B), fitting with previous reports of Ca 2+ -mediated regulation of NO bioavailability in the endothelium (28,29,44,45). Because endothelial NO synthase (eNOS) activity is highly dependent on Ca 2+ and inhibition of eNOS with L-NAME blocked FMD and ACh-mediated NO release in the mutant rats, we propose that Plekha7 is signaling through this pathway; however, additional studies will be needed to determine the connection between Plekha7 and eNOS.…”

“…Flow studies were carried out as described previously (52). NO levels were measured in aortas using DAF-FM diacetate and imaging the fluorescent response to the addition of 2 mM ACh, as described previously (45). Ca 2+ transient studies were performed on aortas loaded with Fluo-4.…”

AT1 Receptors Prevent Salt-Induced Vascular Dysfunction in Isolated Middle Cerebral Arteries of 2 Kidney-1 Clip Hypertensive Rats

“…By contrast, vasodilator responses to ACh and reduced PO 2 that were absent in sham-operated controls fed an HS diet were restored by infusion of ANG II at a dose previously shown to prevent salt-induced ANG II suppression. 16,17,30 Because administration of losartan before the diet change eliminated vascular relaxation in 2K1C rats fed an HS diet, the maintenance of vasodilator responses to ACh and reduced PO 2 in HS-fed 2K1C rats is most likely related to the persisting effects of AT 1 receptor activation to upregulate antioxidant defenses (e.g., Cu/Zn SOD) (Figure 2) in response to the elevated ANG II levels after unilateral renal artery clipping. Those findings provide additional support for the hypothesis that tonic interaction of ANG II with the AT 1 receptor plays an important role in maintaining normal vascular relaxation mechanisms.…”

“…Continuous intravenous infusion of a low dose of ANG II to prevent the salt-induced decrease in plasma ANG II levels not only restores ACh-induced dilation that is lost in cerebral arteries of HS-fed Sprague-Dawley rats [9][10][11]19 but also reduces vascular superoxide levels to NS values and maintains nitric oxide availability in small mesenteric arteries 12 and aortas 30 of HS-fed Sprague-Dawley rats. Low-dose ANG II infusion also prevents the downregulation of Cu/Zn SOD in cerebral arteries of Sprague-Dawley rats fed an HS diet.…”