Channels In Mesenteric Arteries Research Articles

Mechanisms underlying selective coupling of endothelial Ca2+ signals with eNOS vs. IK/SK channels in systemic and pulmonary arteries.

Endothelial cell TRPV4 (TRPV4EC ) channels exert a dilatory effect on the resting diameter of resistance mesenteric and pulmonary arteries. Functional intermediate- and small-conductance K+ (IK and SK) channels and endothelial nitric oxide synthase (eNOS) are present in the endothelium of mesenteric and pulmonary arteries. TRPV4EC sparklets preferentially couple with IK/SK channels in mesenteric arteries and with eNOS in pulmonary arteries. TRPV4EC channels co-localize with IK/SK channels in mesenteric arteries but not in pulmonary arteries, which may explain TRPV4EC -IK/SK channel coupling in mesenteric arteries and its absence in pulmonary arteries. The presence of the nitric oxide-scavenging protein, haemoglobin α, limits TRPV4EC -eNOS signalling in mesenteric arteries. Spatial proximity of TRPV4EC channels with eNOS and the absence of haemoglobin α favour TRPV4EC -eNOS signalling in pulmonary arteries. Spatially localized Ca2+ signals activate Ca2+ -sensitive intermediate- and small-conductance K+ (IK and SK) channels in some vascular beds and endothelial nitric oxide synthase (eNOS) in others. The present study aimed to uncover the signalling organization that determines selective Ca2+ signal to vasodilatory target coupling in the endothelium. Resistance-sized mesenteric arteries (MAs) and pulmonary arteries (PAs) were used as prototypes for arteries with predominantly IK/SK channel- and eNOS-dependent vasodilatation, respectively. Ca2+ influx signals through endothelial transient receptor potential vanilloid 4 (TRPV4EC ) channels played an important role in controlling the baseline diameter of both MAs and PAs. TRPV4EC channel activity was similar in MAs and PAs. However, the TRPV4 channel agonist GSK1016790A (10nm) selectively activated IK/SK channels in MAs and eNOS in PAs, revealing preferential TRPV4EC -IK/SK channel coupling in MAs and TRPV4EC -eNOS coupling in PAs. IK/SK channels co-localized with TRPV4EC channels at myoendothelial projections (MEPs) in MAs, although they lacked the spatial proximity necessary for their activation by TRPV4EC channels in PAs. Additionally, the presence of the NO scavenging protein haemoglobin α (Hbα) within nanometer proximity to eNOS limits TRPV4EC -eNOS signalling in MAs. By contrast, co-localization of TRPV4EC channels and eNOS at MEPs, and the absence of Hbα, favour TRPV4EC -eNOS coupling in PAs. Thus, our results reveal that differential spatial organization of signalling elements determines TRPV4EC -IK/SK vs. TRPV4EC -eNOS coupling in resistance arteries.

Chronic exercise mediates epigenetic suppression of L-type Ca2+ channel and BKCa channel in mesenteric arteries of hypertensive rats.

Regular exercise is a lifestyle intervention for controlling hypertension and has an improving effect on vascular function. Voltage-gated L-type Ca (LTCC) and large-conductance Ca-activated K (BKCa) channels are two principal mediators of vascular smooth muscle cell contractility and arterial tone. The present study tested the hypothesis that DNA methylation dynamics plays a key role in exercise-induced reprogramming and downregulation of LTCC and BKCa channel in mesenteric arteries from spontaneously hypertensive rats (SHRs). SHRs and Wistar-Kyoto (WKY) rats were subjected to exercise training or kept sedentary, and vascular molecular and functional properties were evaluated. Exercise inhibited hypertension-induced upregulation of LTCC and BKCa channel function in mesenteric arteries by repressing LTCC α1c and BKCa β1 subunit expression. In accordance, exercise triggered hypermethylation of α1c and β1 gene in SHR, with concomitant decreasing TET1, increasing DNMT1 and DNMT3b expression in mesenteric arteries, as well as altering peripheral α-KG and S-adenosylmethionine/ S-adenosylhomocysteine ratio. Acting synergistically, these exercise-induced functional and molecular amelioration could allow for attenuating hypertension-induced elevation in arterial blood pressure. Our results indicate that exercise suppresses LTCC and BKCa channel function via hypermethylation of α1c and β1 subunits, which contributes to the restoration of mesenteric arterial function and vasodilation during hypertension.

BKCa channel activity and vascular contractility alterations with hypertension and aging via β1 subunit promoter methylation in mesenteric arteries

Promoter methylation is a key mechanism in the epigenetic reprogramming of gene expression patterns. Here, we investigated the contribution of DNA methylation and the associated expression and function of large-conductance Ca2+-activated K+ (BKCa) channel in mesenteric arteries when hypertension was superimposed on aging. Male Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) at young (12 weeks), adult (36 weeks) and old (64 weeks) life stages were used. BKCa channel currents, BKCa channel activity in regulating vascular tone, and BKCa channel β1 subunit (BKβ1) function and expression were greater in mesenteric arteries from SHR than from age-matched WKY controls. Consistently, hypertension decreased CpG methylation of the BKβ1 promoter at all ages. Furthermore, aging triggered an increase in BKβ1 promoter methylation in both old WKY and SHR, with concomitant suppression of the β1 subunit and BKCa channel activity. Aging enhanced β1 gene promoter methylation and subunit expression without changing BKCa channel function between young and adult WKY animals. In contrast, aging did not alter CpG methylation but facilitated BKCa channel currents and upregulated BKβ1 expression and function in adult SHR. Taken together, our results provide compelling evidence that hypertension and aging exert opposing effects on DNA methylation at BKβ1 promoter, subsequently resulting in different β1 expression levels and functional modulation of mesenteric arterial contractility. Such information is useful in revealing the epigenetic regulation of BKCa channel function in vascular smooth muscle and in comprehensively understanding the molecular mechanisms in vascular physiology and pathophysiology.

Aerobic exercise of low to moderate intensity corrects unequal changes in BK(Ca) subunit expression in the mesenteric arteries of spontaneously hypertensive rats.

Accumulating evidence indicates that hypertension is associated with "ion channel remodeling" of vascular smooth muscle cells (VSMCs). The objective of this study was to determine the effects of exercise intensity/volume on hypertension-associated changes in large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in mesenteric arteries (MAs) from spontaneously hypertensive rats (SHR). Male SHRs were randomly assigned to three groups: a low-intensity aerobic exercise group (SHR-L: 14 m/min), a moderate-intensity aerobic exercise group (SHR-M: 20 m/min), and a sedentary group (SHR). Age-matched Wistar-Kyoto rats (WKYs) were used as normotensive controls. Exercise groups completed an 8-week exercise program. Elevation of the alpha and beta1 proteins was unequal in MA myocytes from SHRs, with the beta1 subunit increasing more than the alpha subunit. BK(Ca) contribution to vascular tone regulation was higher in the myocytes and arteries of SHRs compared to WKYs. SHR BK(Ca) channel subunit protein expression, beta1/alpha ratio, whole cell current density and single-channel open probability was also increased compared with WKYs. Aerobic exercise lowered systemic blood pressure and normalized hypertension-associated BK(Ca) alterations to normotensive control levels in the SHRs. These effects were more pronounced in the moderate-intensity group than in the low-intensity group. There is a dose-effect for aerobic exercise training in the range of low to moderate-intensity and accompanying volume for the correction of the pathological adaptation of BK(Ca) channels in myocytes of MAs from SHR.

Epigenetic regulation of L-type voltage-gated Ca2+ channels in mesenteric arteries of aging hypertensive rats.

Accumulating evidence has shown that epigenetic regulation is involved in hypertension and aging. L-type voltage-gated Ca2+ channels (LTCCs), the dominant channels in vascular myocytes, greatly contribute to arteriole contraction and blood pressure (BP) control. We investigated the dynamic changes and epigenetic regulation of LTCC in the mesenteric arteries of aging hypertensive rats. LTCC function was evaluated by using microvascular rings and whole-cell patch-clamp in the mesenteric arteries of male Wistar-Kyoto rats and spontaneously hypertensive rats at established hypertension (3 month old) and an aging stage (16 month old), respectively. The expression of the LTCC α1C subunit was determined in the rat mesenteric microcirculation. The expression of miR-328, which targets α1C mRNA, and the DNA methylation status at the promoter region of the α1C gene (CACNA1C) were also determined. In vitro experiments were performed to assess α1C expression after transfection of the miR-328 mimic into cultured vascular smooth muscle cells (VSMCs). The results showed that hypertension superimposed with aging aggravated BP and vascular remodeling. Both LTCC function and expression were significantly increased in hypertensive arteries and downregulated with aging. miR-328 expression was inhibited in hypertension, but increased with aging. There was no significant difference in the mean DNA methylation of CACNA1C among groups, whereas methylation was enhanced in the hypertensive group at specific sites on a CpG island located upstream of the gene promoter. Overexpression of miR-328 inhibited the α1C level of cultured VSMCs within 48 h. The results of the present study indicate that the dysfunction of LTCCs may exert an epigenetic influence at both pre- and post-transcriptional levels during hypertension pathogenesis and aging progression. miR-328 negatively regulated LTCC expression in both aging and hypertension.

Enalapril Normalizes Endothelium-Derived Hyperpolarizing Factor-Mediated Relaxation in Mesenteric Artery of Adult Hypertensive Rats Prenatally Exposed to Testosterone.

Prenatal exposure to elevated testosterone levels induces adult life hypertension associated with selective impairments in endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in mesenteric arteries. We tested whether the angiotensin-converting enzyme inhibitor enalapril restores EDHF function through regulating the activities of small (Kcnn3) and intermediate (Kcnn4) conductance calcium-activated potassium channels in mesenteric arteries. Pregnant Sprague-Dawley rats were injected subcutaneously with vehicle or testosterone propionate (0.5 mg/kg/day from Gestation Day 15 to 19), and their 6-mo-old adult male offspring were examined. A subset of rats in these two groups was given enalapril (40 mg/kg/day) for 2 wk through drinking water. Blood pressures were assessed through carotid arterial catheter and endothelium-dependent mesenteric arterial EDHF relaxation, using wire myography. Ace and Kcnn3 and Kcnn4 channel expression levels were also examined. Renal and vascular Ace expression and plasma angiotensin II levels were increased in testosterone offspring. Blood pressure levels were significantly higher in testosterone offspring than in controls, and treatment with enalapril significantly attenuated blood pressure in testosterone offspring. EDHF relaxation in testosterone offspring was reduced compared to that in controls, and it was significantly restored by enalapril treatment. Kcnn4 channel expression and function were similar between control and testosterone rats, but it was not affected by enalapril treatment. Relaxation mediated by Kcnn3 was impaired in testosterone offspring, and it was normalized by enalapril treatment. Furthermore, enalapril treatment restored expression levels of Kcnn3 channels. These findings suggest that enalapril has a positive influence on endothelial function with improvement in EDHF relaxation through normalization of Kcnn3 expression and activity.

Maternal high-salt diets affected pressor responses and microvasoconstriction via PKC/BK channel signaling pathways in rat offspring.

High-salt (HS) intake is linked to hypertension, and prenatal exposure to maternal HS diets may have long-term impact on cardiovascular systems. The relationship between HS diets and cardiovascular disease has received extensive attention. This study determined pressor responses and microvessel functions in the adult offspring rats exposed to prenatal HS. The offspring of 5-month old as young adults in rats were used. Blood pressure, vascular tone, intracellular Ca(2+), and BK channels in mesenteric arteries were measured in the offspring. Phenylephrine (Phe)-induced pressor responses were significantly higher in the prenatal HS offspring. Vessel tension and intracellular Ca(2+) concentrations associated with Phe-induced pressor responses were increased in the mesenteric arteries of the HS offspring. PKC α- and δ-isoforms were upregulated in mesenteric arteries of the HS offspring. The enhanced Phe-mediated vascular activity was linked to the altered PKC-modulated BK channel functions. The results suggested that prenatal exposure to HS altered microvascular activity probably via changes in PKC/BK signaling pathways, which may lead to increased risks of hypertension in the offspring.

Exercise intensity-dependent reverse and adverse remodeling of voltage-gated Ca(2+) channels in mesenteric arteries from spontaneously hypertensive rats.

Exercise can be regarded as a drug for treating hypertension, and the 'dosage' (intensity/volume) is therefore of great importance. L-type voltage-gated Ca(2+) (Cav1.2) channels on the plasma membrane of vascular smooth muscle cells have a pivotal role in modulating the vascular tone, and the upregulation of Cav1.2 channels is a hallmark feature of hypertension. The present study investigated the beneficial and adverse effects of exercise at different intensities on the remodeling of the Cav1.2 channel in mesenteric arteries (MAs) of spontaneously hypertensive rats (SHRs). Moderate- (SHR-M, 18-20 m min(-1)) and high-intensity (SHR-H, 26-28 m min(-1)) aerobic exercise training groups were created for SHRs and lasted for 8 weeks (1 h per day, 5 d per week). Age-matched sedentary SHRs and normotensive Wistar-Kyoto rats (WKY) were used as controls. The mesenteric arterial mechanical and functional properties were evaluated. Moderate-intensity exercise training induced a lower systolic blood pressure and heart rate in these rats compared with sedentary SHRs. BayK 8644 and nifedipine induced vasoconstriction and dose-dependent vasorelaxation, respectively, in the mesenteric arterial rings. Moderate-intensity exercise significantly suppressed the increase in BayK 8644-induced vasoconstriction, tissue sensitivity to nifedipine, Cav1.2 channel current density and Cav1.2 α1C-subunit protein expression in MAs from SHRs. However, high-intensity exercise training aggravated all of these hypertension-associated functional and molecular alterations of Cav1.2 channels. These results indicate that moderate-intensity aerobic training may act as a drug and effectively reverse the remodeling of Cav1.2 channels in hypertension to restore the vascular function in MAs, but that high-intensity exercise exaggerates the adverse remodeling of Cav1.2 channels and worsens the vascular function.

Chronic exercise normalizes changes in Cav 1.2 and KCa 1.1 channels in mesenteric arteries from spontaneously hypertensive rats.

Regular physical activity is an effective non-pharmacological therapy for prevention and control of hypertension. However, the underlying mechanisms are not fully understood. Accumulating evidence shows that the elevated vascular tone in hypertension is a consequence of the 'ion channel remodelling' that occurs during sustained high BP. The present study investigated the effects of aerobic exercise on the electrical remodelling of L-type Ca(2+) (Cav 1.2) and large-conductance Ca(2+) -activated K(+) (KCa 1.1) channels in mesenteric arteries (MAs) from spontaneously hypertensive rats (SHRs). SHRs and normotensive (Wistar-Kyoto) rats were subjected to aerobic training or kept sedentary, and vascular mechanical and functional properties were evaluated. Exercise did not affect the heart weight, but reduced the heart rate and body weight in SHR. In mesenteric arterial myocytes, exercise normalized the increased Cav 1.2 and KCa 1.1 current density in SHRs. Exercise also ameliorated the increased open probability and mean open time of the single KCa 1.1 channel in hypertension. The isometric contraction study revealed that both nifedipine (Cav 1.2 channel blocker) and NS11021 (KCa 1.1 channel activator) induced concentration-dependent vasorelaxation in MAs precontracted with noradrenaline. Exercise normalized the increased sensitivity of tissues to nifedipine and NS11021 in SHR. Furthermore, protein expression of the Cav 1.2 α1C -subunit together with the KCa 1.1 α- and β1-subunit was significantly increased in SHRs; and exercise ameliorated these molecular alterations in hypertension. Chronic exercise reduces BP and restores vascular function in MAs from SHR, which might be related to the correction of the Cav 1.2 and KCa 1.1 channel remodelling during hypertension.

Exercise Training Reverses Unparallel Downregulation of MaxiK Channel - and 1-Subunit to Enhance Vascular Function in Aging Mesenteric Arteries

This study was designed to determine the effects of aerobic exercise training on aging-associated selective changes of the function and expression of the large-conductance Ca(2+)-activated K(+) (MaxiK) channels in mesenteric arteries. Male Wistar rats aged 19-21 months were randomly assigned to sedentary (O-SED) and exercise-trained groups (O-EX). Two-month-old rats were used as Young control. Addition of iberiotoxin (10(-8) M) increased the norepinephrine-induced arterial contraction in all three groups, with the greatest enhancement being in Young and the least in O-SED. Patch clamp study revealed the characteristics of aging on MaxiK channel function in mesenteric arteries, mainly including (a) decrease of iberiotoxin-sensitive whole-cell K(+) current, (b) decrease of open probability and Ca(2+)/voltage sensitivity of single MaxiK channel, and (c) reduction of tamoxifen-induced MaxiK activation. After exercise training, all of these changes were markedly inhibited. Western blotting revealed that the protein expression of MaxiK was significantly reduced with aging and the suppression of β1-subunit was larger than that of α-subunit, although exercise training diminished this alteration. Taken together, aerobic exercise training reverses the aging-related unparallel downregulation of MaxiK α- and β1-subunit expression on mesenteric arteries, which partly underlies the beneficial effect of exercise on restoring aging-associated reduction in mesenteric artery vasodilatory properties.

Effect of a diet rich in fat and/or fructose on potassium channel gene expression in rat small mesenteric artery

We tested if arterial K+ channel gene expression is reduced under dietary conditions mimicking the metabolic syndrome. Male Sprague‐Dawley rats were fed high‐fat + high‐fructose (HFF; N=4) or high‐fructose (HF; N=4) diet from 4 to 32 weeks (wks) of age. Age‐matched control rats (CTRL) were fed normal chow (N=4 in each group). Systolic blood pressure (SBP) was measured using the tail cuff method. mRNA expression of K+ channels in mesenteric arteries was measured using quantitative real‐time polymerase chain reaction (Q‐PCR). At 32 wks body weight (BW) was increased in HFF (639±37g; P<0.05) compared to CTRL (522±22g), whereas BW was similar in HF (574±35g) and CTRL (564±15g). Average SBP through wks 10–32 was higher in both HFF and HF rats compared to their respective CTRL (HFF: 134±4 mmHg vs. 121±2 mmHg, P<0.05; and HF: 131±5 mmHg vs. 118±2 mmHg, P<0.05). In small mesenteric artery of HFF rats, mRNA expression of SK3 was reduced to 59% of that in CTRL (P<0.05) and KV1.5 was reduced to 73% of that in CTRL (P<0.01), while Kir2.1, Kir6.1, BKCa, IKCa, KV1.2 and KV7.4 expression was unchanged. HF diet did not significantly change K+ channel expression. We conclude that reduced expression of SK3 and KV1.5 channels might partially explain the increased SBP in metabolically challenged rats fed a diet rich in fructose + fat but not in those fed high‐fructose only.Grants: Danish National Research Foundation (F.); Danish Heart F.; Lundbeck F.

Potassium ATP channel function is altered in mesenteric arteries of old high salt fed rats

Hypertension is a risk factor for cardiovascular disease and dietary salt is a contributing factor to high blood pressure. Increased salt intake in the elderly has been shown to impair relaxation of resistance vessels. Therefore, we examined whether a high salt (HS) diet alters the function of KATP channels in mesenteric arteries (MAs) from young and old rats. Young (7 mo) and old (29 mo) F‐344xBN rats were fed a control or HS diet (8% NaCl) for 12 days and 2nd order MAs were used for vascular measurements. Acetylcholine (Ach)‐induced relaxation was significantly reduced with age. Relaxation to Ach was 92 ± 2% in young vs. 81 ± 4% in old arteries. Pretreatment with the KATP channel blocker glibenclamide only reduced relaxation to Ach in young MAs. On a HS diet, dilation to Ach was reduced in old salt MAs (60 ± 3%) when compared with old control arteries (81 ± 4%; P<0.001). Glibenclamide reduced Ach‐induced dilation in young salt MAs but had no effect on old salt MAs. Cromakalim (KATP channel opener) dilation was reduced in old salt MAs when compared with old control arteries. Maximal relaxation to cromakalim was 99 ± 1% in old control vs. 85 ± 5% in old salt arteries (P<0.05). These findings demonstrate that age impairs endothelium‐dependent dilation in MAs. Furthermore, a HS diet alters the function of KATP channels in isolated MAs and affects the mediation of dilator stimuli.Supported by the Medical Research Service of the Department of Veterans Affairs and NIA T32 AG000196 award.

Losartan Normalizes Endothelium-Derived Hyperpolarizing Factor–Mediated Relaxation by Activating Ca2+-Activated K+ Channels in Mesenteric Artery From Type 2 Diabetic GK Rat

Ca2+-activated K+ (K Ca ) channels are important for endothelium-derived hyperpolarizing factor (EDHF) signaling. Since treatment with angiotensin II receptor blockers (ARBs) improves vasculopathies in type 2 diabetic patients, we asked whether the EDHF-type relaxation and its associated K Ca channels [small (SK Ca )–, intermediate (IK Ca )–, and large (BK Ca )–conductance channels] are abnormal in mesenteric arteries isolated from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes (34 – 38 weeks) and whether an ARBs (losartan, 25 mg · kg−1 · day−1 for 2 weeks) might correct these abnormalities. Although the acetylcholine chloride–induced EDHF-type relaxation in mesenteric arteries from GK rats was reduced versus the Wistar controls, it was significantly restored by losartan treatment. The SK Ca-blocker apamin or the IK Ca-blocker 1-[(2-chlorophenyl)diphenylmethyl]-1 H-pyrazole (TRAM-34) inhibited such relaxations in the losartan-treated or -untreated Wistar groups and in the losartan-treated GK group, but not in the losartan-untreated GK group. The BK Ca-blocker iberiotoxin had a significant inhibitory effect in only one of these groups, the losartan-treated GK. The relaxations induced by the SK Ca /IK Ca acti-vator NS309 and the BK Ca activator NS1619, which were impaired in GK rats, were normalized by losartan treatment. We conclude that losartan improves EDHF-type relaxation in GK rats at least partly by normalizing SK Ca /IK Ca activities and increasing BK Ca activity.

High-fat diet may impair K ATP channels in vascular smooth muscle cells

K ATP channel in vascular smooth muscle cell (VSMC) is closely linked to the etiology of hypertension. The aim of this study was to investigate effect of the high-fat diet-induced obesity on K ATP channel and blood pressure. Obesity was induced by a 24-week high-fat diet feeding in rats. Function and expression of K ATP channel in mesenteric arteries were examined using myography system, patch clamp and Western blotting. We show that high-fat diet increased blood pressure, decreased K ATP channel-mediated relaxation responses and currents, and down-regulated K ATP expression in VSMC. In conclusion, diet-induced obesity impairs K ATP channels in VSMC, which may underscore obesity-triggered increase in blood pressure.

Recovery of impaired K+ channels in mesenteric arteries from spontaneously hypertensive rats by prolonged treatment with cholecalciferol.

1. The mechanism responsible for blood pressure reduction in spontaneously hypertensive rats (SHR) after prolonged cholecalciferol treatment was studied. Two-week treatment of SHR with 0.125 mg cholecalciferol kg-1 body weight per day orally caused significant reductions of systolic blood pressure and of the resting perfusion pressure of the mesenteric vascular bed at constant flow. 2. In addition, the treated animals presented a normalization of the maximum vasoconstriction response to noradrenaline and a reduction of the maximum effect of the adrenaline concentration-response curves. This latter effect probably was due to recovery of the impaired Ca(2+)-dependent K+ channels coupled to alpha 2-adrenoceptors since it was prevented by apamin. 3. The treatment with cholecalciferol also normalized the smooth muscle cell membrane potential of de-endothelialized mesenteric arteries of SHR and their hyperpolarizing responses to alpha 2-adrenergic agonists, which were depressed in untreated SHR. 4. In mesenteric rings with endothelium, alpha 2-adrenergic agonists caused similar hyperpolarizing responses in the SHR and in normotensive Wistar (NWR) and Wistar Kyoto (WKY). In non cholecalciferol-treated SHR the hyperpolarizing mediator involved in this effect was NO, while in NWR it was the endothelium-derived hyperpolarizing factor (EDHF). After cholecalciferol treatment, the hyperpolarization induced by alpha 2-adrenergic agonists in SHR smooth muscle cells was mediated by EDHF, as in NWR. 5. Our results indicate that the hypotensive effect of cholecalciferol in the SHR is probably due to the normalization of vascular reactivity, by restoring the functioning of apamin- and ATP-sensitive K+ channels located in the vascular smooth muscle cell membrane, which are impaired in the SHR.