Yasuo Kansui

Critical role of gap junctions in endothelium-dependent hyperpolarization in rat mesenteric arteries

1. Acetylcholine (ACh) evokes endothelium‐dependent hyperpolarization in arterial cells, presumably through endothelium‐derived hyperpolarizing factor (EDHF). The identity of EDHF is still elusive; however, several recent studies suggest the possible involvement of myoendothelial gap junctions in the EDHF response.

Angiotensin II receptor antagonist improves age-related endothelial dysfunction.

Background We previously demonstrated that the angiotensin converting enzyme (ACE) inhibitor, enalapril, prevents the age-related impairment of endothelium-dependent hyperpolarization and relaxation mediated by endothelium-derived hyperpolarizing factor (EDHF). Objective To test whether angiotensin II type 1 (AT1) receptor antagonists would also improve age-related endothelial dysfunction. Methods Normotensive Wistar–Kyoto (WKY) rats were treated for 3 months with either the AT1 receptor antagonist, candesartan cilexetil (3.5 mg/kg per day; candesartan group), or the ACE inhibitor, enalapril (20 mg/kg per day; enalapril group), from 9 to 12 months of age. Untreated 12-month-old WKY rats (old group) served as controls (n = 7–12). Results The two treatments decreased systolic blood pressure comparably. EDHF-mediated hyperpolarization in response to acetylcholine (ACh; 10−5 mol/l) in the presence of norepinephrine in mesenteric arteries was improved in both the candesartan and enalapril groups to a similar extent compared with the old group (candesartan group, −24 ± 3 mV; enalapril group, −21 ± 2 mV; old group, −13 ± 2 mV). EDHF-mediated relaxation was similarly improved in the candesartan and enalapril groups (maximum relaxation: candesartan group, 70 ± 7%; enalapril group, 63 ± 8%; old group, 33 ± 9%). Hyperpolarization and relaxation responses to levcromakalim, an ATP-sensitive K+-channel opener, were similar in all groups. Conclusions These findings suggest that the AT1 receptor antagonist is as effective as the ACE inhibitor in improving the age-related decline in EDHF-mediated hyperpolarization and relaxation in normotensive rats. Thus AT1 receptor antagonists might serve as novel tools with which to prevent endothelial dysfunction associated with aging.

Changes in endothelium‐derived hyperpolarizing factor in hypertension and ageing: response to chronic treatment with renin–angiotensin system inhibitors

1. Endothelial function is impaired in hypertension and ageing and this may be associated with an increase in cardiovascular disease. Several clinical studies have shown that blocking the renin–angiotensin system (RAS) improves endothelial function not only in hypertensive patients, but also in normotensive patients with cardiovascular disease.

EFFECTS OF FLUVASTATIN ON ENDOTHELIUM‐DERIVED HYPERPOLARIZING FACTOR‐ AND NITRIC OXIDE‐MEDIATED RELAXATIONS IN ARTERIES OF HYPERTENSIVE RATS

1. Endothelial cells release endothelium‐derived hyperpolarizing factor (EDHF), as well as nitric oxide (NO). It has recently been suggested that 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase inhibitors (statins) improve NO‐mediated endothelial function, partially independently of their cholesterol‐lowering effects. It is, however, unclear whether statins improve EDHF‐mediated responses.

Mice Heterozygous for the Xanthine Oxidoreductase Gene Facilitate Lipid Accumulation in Adipocytes

Objective— Xanthine oxidoreductase (XOR) catalyzes the production of uric acid with concomitant generation of reactive oxygen species. XOR has been shown to regulate adipogenesis through the control of peroxisome proliferator–activated receptor &ggr;, but its role in adipose tissue remains unclear. The aim of this study was to examine the role of XOR in adipose tissue using XOR genetically modified mice. Approach and Results— Experiments were performed using 2-, 4-, and 18-month-old XOR heterozygous mice (XOR+/−) and their wild-type littermates to evaluate the physiological role of XOR as the mice aged. Stromal vascular fraction cells were prepared from epididymal white adipose tissue in 2-month-old XOR mice to assess adipogenesis. At 18 months, XOR+/− mice had significantly higher body weight, higher systolic blood pressure, and higher incidence of insulin resistance compared with wild-type mice. At 4 months, blood glucose and the expressions of CCAAT enhancer–binding protein &bgr;, peroxisome proliferator–activated receptor &ggr;, monocyte chemoattractant protein-1, and tumor necrosis factor &agr; mRNA in epididymal white adipose tissue were significantly higher in XOR+/− than in wild-type mice. Furthermore, histological analysis of epididymal white adipose tissue in XOR+/− mice revealed that adipocyte size and the F4/80-positive macrophage count were increased. Experiments with a high-fat diet exhibited that body weight gain was also significantly higher in XOR+/− than in wild-type mice. In stromal vascular fraction cells derived from XOR+/− mice, the levels of peroxisome proliferator–activated receptor &ggr;, fatty acid–binding protein 4, and CCAAT enhancer–binding protein &agr; mRNA were upregulated, and oxidative stress levels were elevated during differentiation into adipocytes. Conclusions— These results suggest that the reduction in XOR gene expression in mice augments lipid accumulation in adipocytes, accompanied by an increase in oxidative stress, and induces obesity with insulin resistance in older age.

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

This study was designed to determine whether a high-salt diet would alter endothelial function and, if so, the relative contributions of endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide (NO) to any changes in vasomotor responses. Male Dahl salt-sensitive (DS) rats were given either a high-salt diet (8% NaCl, DS-H) or a low-salt diet (0.4% NaCl, DS-L) for 6 weeks. Membrane potentials and contractile responses were recorded from the isolated superior mesenteric arteries. After salt loading, DS-H developed hypertension, while DS-L remained normotensive. No difference was found in acetylcholine (ACh)-induced, endothelium-dependent relaxation between the groups. However, after treatment with indomethacin and NO synthase inhibitor, EDHF-like relaxation was significantly greater in DS-H than in DS-L. In contrast, NO-mediated relaxation was significantly smaller in DS-Hthan in DS-L. Iberiotoxin (IbTx), a specific blocker of large-conductance calcium-dependent potassium (BKCa) channels, attenuated EDHF-like relaxation in DS-H but not in DS-L. IbTx marginally inhibited EDHF-mediated hyperpolarization only in DS-H. Endothelium-independent relaxation in response to sodium nitroprusside or levcromakalim was similar in both groups. In conclusion, EDHF-like relaxation is upregulated through the activation of BKCa channels in the mesenteric arteries of DS-H. As the overall relaxation in response to ACh did not differ between the groups, the upregulation of EDHF appears to compensate for the loss of NO in the mesenteric arteries of DS-H.

Effects of angiotensin II receptor antagonist on impaired endothelium-dependent and endothelium-independent relaxations in type II diabetic rats

Background Diabetes mellitus is an important risk factor for cardiovascular diseases, and vasodilator dysfunction may contribute to vascular complications in diabetes. We previously demonstrated that the angiotensin II receptor blocker (ARB) corrected the impaired endothelium-derived hyperpolarizing factor (EDHF)-mediated arterial hyperpolarization and relaxation associated with hypertension or aging, partially independently of blood pressure. Objective To test whether EDHF-mediated, as well as endothelium-independent, relaxations would be altered in arteries from type II diabetic Goto–Kakizaki rats, and whether ARB would correct these alterations. Methods Goto–Kakizaki rats were treated with either the ARB candesartan or a combination of hydralazine and hydrochlorothiazide for 8 weeks, beginning at 10 weeks of age. Membrane potentials and contractile responses were recorded from the isolated mesenteric arteries. Results The two treatments lowered blood pressure comparably. Acetylcholine-induced, EDHF-mediated hyperpolarization and relaxation in mesenteric arteries were markedly impaired in untreated Goto–Kakizaki rats compared with age-matched Wistar rats, and neither ARB nor the combination therapy improved these responses. On the other hand, relaxations to endothelium-derived nitric oxide, assessed in rings precontracted with high potassium solution, were similar among the four groups. Relaxation to the nitric oxide donor sodium nitroprusside and that to levcromakalim, an ATP-sensitive K+-channel opener, were also impaired in untreated Goto–Kakizaki rats, and the response to sodium nitroprusside was partially improved in treated Goto–Kakizaki rats. Conclusions These findings suggest that EDHF-mediated hyperpolarization and relaxation and endothelium-independent relaxations are both impaired in arteries of type II diabetic rats, and antihypertensive treatment with or without ARB partially corrects endothelium-independent relaxations to the nitric oxide donor but not EDHF-mediated responses.

Prolongation of the QT interval in primary aldosteronism.

1. Only limited information is available concerning the changes in the electrocardiogram in primary aldosteronism. The aim of the present study was to determine factors influencing the QTc interval in patients with primary aldosteronism.

Downregulation of Endothelial Transient Receptor Potential Vanilloid Type 4 Channel and Small-Conductance of Ca2+-Activated K+ Channels Underpins Impaired Endothelium-Dependent Hyperpolarization in Hypertension

Endothelium-dependent hyperpolarization (EDH)–mediated responses are impaired in hypertension, but the underlying mechanisms have not yet been determined. The activation of small- and intermediate-conductance of Ca2+-activated K+ channels (SKCa and IKCa) underpins EDH-mediated responses. It was recently reported that Ca2+ influx through endothelial transient receptor potential vanilloid type 4 channel (TRPV4) is a prerequisite for the activation of SKCa/IKCa in endothelial cells in specific beds. Here, we attempted to determine whether the impairment of EDH in hypertension is attributable to the dysfunction of TRPV4 and S/IKCa, using isolated superior mesenteric arteries of 20-week-old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wistar–Kyoto (WKY) rats. In the WKY arteries, EDH-mediated responses were reduced by a combination of SKCa/IKCa blockers (apamin plus TRAM-34; 1-[(2-chlorophenyl)diphenylmethl]-1H-pyrazole) and by the blockade of TRPV4 with the selective antagonist RN-1734 or HC-067047. In the SHRSP arteries, EDH-mediated hyperpolarization and relaxation were significantly impaired when compared with WKY. GSK1016790A, a selective TRPV4 activator, evoked robust hyperpolarization and relaxation in WKY arteries. In contrast, in SHRSP arteries, the GSK1016790A-evoked hyperpolarization was small and relaxation was absent. Hyperpolarization and relaxation to cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine, a selective SKCa activator, were marginally decreased in SHRSP arteries compared with WKY arteries. The expression of endothelial TRPV4 and SKCa protein was significantly decreased in the SHRSP mesenteric arteries compared with those of WKY, whereas function and expression of IKCa were preserved in SHRSP arteries. These findings suggest that EDH-mediated responses are impaired in superior mesenteric arteries of SHRSP because of a reduction in both TRPV4 and SKCa input to EDH.

Chronic fluvastatin treatment alters vascular contraction by inhibiting the Rho/Rho-kinase pathway.

1 In the present study, we investigated the effects of chronic treatment of stroke‐prone spontaneously hypertensive rats (SHRSP) with the statin fluvastatin on vascular Rho/Rho‐kinase pathway mediated contraction, which has been shown to be upregulated in hypertension. 2 Contribution of the Rho/Rho‐kinase pathway to noradrenaline‐induced contraction of arteries from SHRSP was assessed by the inhibitory effect of Y‐27632, a Rho/Rho‐kinase inhibitor. Stroke‐prone spontaneously hypertensive rats were treated with fluvastatin (10 mg/kg per day) for 1 month. 3 Treatment with fluvastatin tended to attenuate the contraction to noradrenaline and significantly decreased the Y‐27632‐sensitive component of the contraction in controls compared with fluvastatin‐treated rats. 4 RhoA, as assessed by western blotting, was also reduced by fluvastatin treatment. 5 These findings suggest that chronic treatment with fluvastatin reduces the contractile response associated with Rho/Rho‐kinase in arteries of hypertensive rats.