Contribution of sarcoplasmic reticulum calcium uptake and L-type calcium channels to altered vascular responsiveness in the aorta of renal hypertensive rats

C-type natriuretic peptide-induced relaxation through cGMP-dependent protein kinase and SERCA activation is impaired in two kidney-one clip rat aorta

AIMS

Hypertension underlies endothelial dysfunction, and activation of vasorelaxation signaling with low dependence on nitric oxide (NO) represents a good alternative for vascular modulation. C-type natriuretic peptide (CNP) causes relaxation by increasing cyclic guanosine 3',5'-monophosphate (cGMP) or Gi-protein activation through its natriuretic peptide receptor-B or -C, respectively. We have hypothesized that CNP could exerts its effects and could overcome endothelial dysfunction in two kidney-one clip (2K-1C) hypertensive rat aorta. Here, we investigate the intracellular signaling involved in CNP effects in hypertension.

MATERIALS AND METHODS

The 2K-1C hypertension was induced in male Wistar rats (200 g). CNP-induced vascular relaxation and cGMP production were investigated in rat thoracic aortas. The natriuretic peptide receptor-B and -C localization was evaluated by immunofluorescence. Calcium mobilization was assessed in endothelial cells from rat aortas.

KEY FINDINGS

CNP induced similar relaxation in normotensive and 2K-1C hypertensive rat aortas, which increased after endothelium removal. CNP-induced relaxation involved natriuretic peptide receptor-B and -C activation in 2K-1C rats. Nitric oxide synthase (NOS) and soluble guanylyl cyclase (sGC) counter-regulated CNP-particulate GC (pGC) activation in aortas. CNP reduced endothelial calcium and increased cGMP production, which was lower in 2K-1C. CNP-induced cGMP-dependent protein kinase (PKG) and sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activation was impaired in 2K-1C rat aorta.

SIGNIFICANCE

Our results indicated CNP triggered relaxation through its natriuretic peptide receptor-B and -C in 2K-1C rat aortas, and that CNP-induced relaxation overcomes endothelial dysfunction in hypertension. In addition, NOS and sGC activities counter-regulate CNP-pGC activation to induce vascular relaxation.

Equilin displays similar endothelium-independent vasodilator potential to 17β-estradiol regardless of lower potential to inhibit calcium entry

Conjugated equine estrogens (CEE) have been widely used by women who seek to relieve symptoms of menopause. Despite evidence describing protective effects against risk factors for cardiovascular diseases by naturally occurring estrogens, little is known about the vascular effects of equilin, one of the main components of CEE and not physiologically present in women. In this regard, the present study aims to compare the vascular effects of equilin in an experimental model of hypertension with those induced by 17β-estradiol. Resistance mesenteric arteries from female spontaneously hypertensive rats (SHR) were used for recording isometric tension in a small vessel myograph. As effectively as 17β-estradiol, equilin evoked a concentration-dependent relaxation in mesenteric arteries from female SHRs contracted with KCl, U46619, PDBu or ET-1. Equilin-induced vasodilation does not involve classical estrogen receptor activation, since the estrogen receptor antagonist (ICI 182,780) failed to inhibit relaxation in U46619-precontracted mesenteric arteries. Vasorelaxation was not affected by either endothelium removal or by inhibiting the release or action of endothelium-derived factors. Incubation with L-NAME (NOS inhibitor), ODQ (guanylyl cyclase inhibitor) or KT5823 (inhibitor of protein kinase G) did not affect equilin-induced relaxation. Similarly, indomethacin (COX inhibitor) or blockage of potassium channels with tetraethylammonium, glibenclamide, 4-aminopyridine, or ouabain did not affect equilin-induced relaxation. Inhibitors of adenylyl cyclase SQ22536 or protein kinase A (KT5720) also had no effects on equilin-induced relaxation. While 17β-estradiol inhibited calcium (Ca²⁺) -induced contractions in high-K⁺ depolarization medium in a concentration-dependent manner, equilin induced a slight rightward-shift in the contractile responses to Ca²⁺. Comparable pattern of responses were observed in the concentration-response curves to (S)-(-)-Bay K 8644, a L-type Ca²⁺ channel activator. Equilin was unable to block the transitory contraction produced by caffeine-induced Ca²⁺ release from intracellular stores. In conclusion, equilin blocks L-type Ca²⁺ channels less effectively than 17β-estradiol. Despite its lower effectiveness, equilin equally relaxes resistance mesenteric arteries by blocking Ca²⁺ entry on smooth muscle.

Chronic stress improves NO- and Ca2+ flux-dependent vascular function: a pharmacological study

Background

Stress is associated with cardiovascular diseases.

Objective

This study aimed at assessing whether chronic stress induces vascular alterations, and whether these modulations are nitric oxide (NO) and Ca2+ dependent.

Methods

Wistar rats, 30 days of age, were separated into 2 groups: control (C) and Stress (St). Chronic stress consisted of immobilization for 1 hour/day, 5 days/week, 15 weeks. Systolic blood pressure was assessed. Vascular studies on aortic rings were performed. Concentration-effect curves were built for noradrenaline, in the presence of L-NAME or prazosin, acetylcholine, sodium nitroprusside and KCl. In addition, Ca²⁺ flux was also evaluated.

Results

Chronic stress induced hypertension, decreased the vascular response to KCl and to noradrenaline, and increased the vascular response to acetylcholine. L-NAME blunted the difference observed in noradrenaline curves. Furthermore, contractile response to Ca²⁺ was decreased in the aorta of stressed rats.

Conclusion

Our data suggest that the vascular response to chronic stress is an adaptation to its deleterious effects, such as hypertension. In addition, this adaptation is NO- and Ca²⁺-dependent. These data help to clarify the contribution of stress to cardiovascular abnormalities. However, further studies are necessary to better elucidate the mechanisms involved in the cardiovascular dysfunction associated with stressors. (Arq Bras Cardiol. 2014; [online].ahead print, PP.0-0)

Ruthenium complexes as NO donors for vascular relaxation induction

Nitric oxide (NO) donors are substances that can release NO. Vascular relaxation induction is among the several functions of NO, and the administration of NO donors is a pharmacological alternative to treat hypertension. This review will focus on the physicochemical description of ruthenium-derived NO donor complexes that release NO via reduction and light stimulation. In particular, we will discuss the complexes synthesized by our research group over the last ten years, and we will focus on the vasodilation and arterial pressure control elicited by these complexes. Soluble guanylyl cyclase (sGC) and potassium channels are the main targets of the NO species released from the inorganic compounds. We will consider the importance of the chemical structure of the ruthenium complexes and their vascular effects.

Effects of spaceflight and ground recovery on mesenteric artery and vein constrictor properties in mice

Following exposure to microgravity, there is a reduced ability of astronauts to augment peripheral vascular resistance, often resulting in orthostatic hypotension. The purpose of this study was to test the hypothesis that mesenteric arteries and veins will exhibit diminished vasoconstrictor responses after spaceflight. Mesenteric arteries and veins from female mice flown on the Space Transportation System (STS)-131 (n=11), STS-133 (n=6), and STS-135 (n=3) shuttle missions and respective ground-based control mice (n=30) were isolated for in vitro experimentation. Vasoconstrictor responses were evoked in arteries via norepinephrine (NE), potassium chloride (KCl), and caffeine, and in veins through NE across a range of intraluminal pressures (2-12 cmH(2)O). Vasoconstriction to NE was also determined in mesenteric arteries at 1, 5, and 7 d postlanding. In arteries, maximal constriction to NE, KCl, and caffeine were reduced immediately following spaceflight and 1 d postflight. Spaceflight also reduced arterial ryanodine receptor-3 mRNA levels. In mesenteric veins, there was diminished constriction to NE after flight. The results indicate that the impaired vasoconstriction following spaceflight occurs through the ryanodine receptor-mediated intracellular Ca(2+) release mechanism. Such vascular changes in astronauts could compromise the maintenance of arterial pressure during orthostatic stress.

Simulated microgravity alters rat mesenteric artery vasoconstrictor dynamics through an intracellular Ca2+release mechanism

Previous work has shown that orthostatic hypotension associated with cardiovascular deconditioning results from inadequate peripheral vasoconstriction. We used the hindlimb-unloaded (HU) rat in this study as a model to induce cardiovascular deconditioning. The purpose of this study was to test the hypothesis that 14 days of HU diminishes vasoconstrictor responsiveness of mesenteric resistance arteries. Mesenteric resistance arteries from control ( n = 43) and HU ( n = 44) rats were isolated, cannulated, and pressurized to 108 cm H2O for in vitro experimentation. Myogenic (intralumenal pressure ranging from 30 to 180 cm H2O), KCl (2–100 mM), norepinephrine (NE, 10−9–10−4M) and caffeine (1–20 mM) induced vasoconstriction, as well as the temporal dynamics of vasoconstriction to NE, were determined. The active myogenic and passive pressure responses were unaltered by HU when pressures remained within physiological range. However, vasoconstrictor responses to KCl, NE, and caffeine were diminished by HU, as well as the rate of constriction to NE (C, 14.8 ± 3.6 μm/s vs. HU 7.6 ± 1.8 μm/s). Expression of sarcoplasmic reticulum Ca2+ATPase 2 and ryanodine 3 receptor mRNA was unaffected by HU, while ryanodine 2 receptor mRNA and protein expression were diminished in mesenteric arteries from HU rats. These data suggest that HU-induced and microgravity-associated orthostatic intolerance may be due, in part, to an attenuated vasoconstrictor responsiveness of mesenteric resistance arteries resulting from a diminished ryanodine 2 receptor Ca2+release mechanism.

Altered vascular reactivity in mice made hypertensive by nitric oxide synthase inhibition

This study tested the hypothesis that nitric oxide (NO) synthase inhibition in mice would result in hypertension characterized by increased agonist-induced vasoconstrictor responsiveness and attenuated endothelium-dependent vasodilation. Administration of N-nitro-L-arginine (L-NNA), an NO synthase inhibitor (1 g/L, 4 weeks), via drinking water to mice resulted in significant elevations in blood pressure. Phenylephrine-induced contraction was significantly increased in aortic rings from L-NNA-treated mice compared with rings from control mice. Aortic rings from control mice showed a concentration-dependent relaxation to acetylcholine whereas those obtained from L-NNA-treated mice showed a biphasic response, contracting at lower concentrations while relaxing at higher concentrations. Aortic rings from L-NNA-treated mice had decreased relaxation to acetylcholine and increased sensitivity to sodium nitroprusside compared with control rings. The relaxation induced by an NO-independent soluble guanylyl cyclase activator was not different between groups. In aortic rings from control and L-NNA-treated mice pre-contracted with phenylephrine, the administration of L-NNA to the organ bath caused additional and sustained contraction. When compared with the contraction induced by phenylephrine, L-NNA-induced contraction in aorta from control mice was significantly higher than that in aorta from L-NNA-treated mice. We conclude that mice treated with L-NNA develop hypertension and that a reduction in NO availability is responsible for the changes observed in vascular reactivity.

Changes in the vascular beta-adrenoceptor-activated signalling pathway in 2Kidney-1Clip hypertensive rats

1. beta-Adrenoceptor (beta-AR)-mediated vasodilation, which plays an important physiological role in the regulation of vascular tone, is decreased in two-kidney, one clip (2K-1C) renal hypertension. In this study, downstream pathways related to vascular beta-AR activation were evaluated in 2K-1C rats. 2. Relaxation responses to isoprenaline, forskolin and 8-Br-cAMP were diminished in aortas without endothelium from 2K-1C when compared to those in normotensive two kidney (2K). Basal adenosine-3',5'-monophosphate (cAMP), as well as isoprenaline-induced increase in cAMP levels, was not different between 2K and 2K-1C aortas. 3. Contractile responses to caffeine, after depletion and reloading of intracellular Ca(2+) stores, were greater in 2K-1C than in 2K. The presence of isoprenaline during the Ca(2+)-reloading period abolished the differences between groups by increasing caffeine contraction in 2K without changing this response in 2K-1C aortas. Inhibition of the sarcolemmal Ca(2+)ATPase with thapsigargin markedly attenuated isoprenaline vasodilation in both 2K and 2K-1C and abolished the differences between groups. 4. Blockade of ATP-sensitive K(+) channels (K(ATP)) channels with glibenclamide significantly decreased isoprenaline vasodilation in 2K-1C without affecting this response in 2K. Both vascular gene and protein expression of protein kinase A (PKA), as well as phosphoserine-containing proteins, were increased in 2K-1C vs 2K rats. 5. In conclusion, decreased isoprenaline vasodilation in 2K-1C hypertensive rats is related to impaired modulation of the sarcolemmal Ca(2+)ATPase activity. Moreover, K(ATP) channels may play a compensatory role on isoprenaline-induced relaxation in renal hypertension. Both Ca(2+)ATPase and K(ATP) channel functional alterations, associated with decreased beta-AR vasodilation, are paralleled by an upregulation of protein kinase A (PKA) and phosphoserine proteins expression.

Endothelin-1-induced contraction is impaired in the tail artery of renal hypertensive rats

The contraction induced by endothelin-1 (ET-1) was evaluated in tail arteries from normotensive two-kidney (2K) and hypertensive two-kidney-one-clip (2K-1C) rats. Since the maximal effect induced by ET-1 (0.1-30 or 100 nmol/l) was lower in 2K-1C (1.11 +/- 0.10 g) than in 2K (1.46 +/- 0.14 g) tail arteries, we evaluated the possible mechanisms involved in this blunted response. The sensitivity and efficacy of ET-1 were not affected by endothelium removal in either group. ET-1 failed to induce contraction of 2K and 2K-1C arteries in Ca(2+)-free medium. The contractile response induced by 10 nmol/l ET-1 was similarly inhibited by 0.1 microM nifedipine in arteries from 2K (81.6 +/- 3.3%) and 2K-1C (81.3 +/- 3.8%) rats. The effect of nifedipine was not potentiated by 10 mumol/l SK&F 96365. The cytosolic Ca2+ concentration ([Ca2+]c) was similarly increased by 30 nmol/l ET-1 in smooth muscle cells isolated from tail arteries of 2K (30.80 +/- 11.94 nmol/l) and 2K-1C (54.06 +/- 10.98 nmol/l) rats. In conclusion, the blunted contraction induced by ET-1 in 2K-1C tail arteries was not dependent on the endothelium or on decreased Ca2+ influx through channels sensitive to nifedipine or SK&F 96365. Since the increase of [Ca2+]c upon stimulation with ET-1 was similar in 2K and 2K-1C tail artery cells, probably the sensitivity to Ca2+ is decreased in 2K-1C tail arteries.

Ca(2+) influx is increased in 2-kidney, 1-clip hypertensive rat aorta

Arteries from hypertensive rats show a greater contraction in response to Ca(2+) channel activator and an increased sensitivity to Ca(2+) entry blockers compared with those of normotensive rats. These facts suggest an altered Ca(2+) influx through membrane channels. In this study, this hypothesis was tested by direct activation of voltage-gated Ca(2+) channels using Bay K 8644, a dihydropyridine sensitive large conductance (L-type) Ca(2+) channel opener in aortas from 2-kidney, 1-clip (2K1C) hypertensive rats. Because the membrane potential of smooth muscle cells is an important regulator of the conformational state of L-type Ca(2+) channels and, consequently, dihydropyridine affinity, the effect of 10 mmol/L KCl on the responses to Bay K 8644 was also studied. Maximal contraction (ME) and sensitivity to Bay K 8644 were greater in 2K1C rats than in 2K normotensive rats (ME, 1.77+/-0.15 versus 1.25+/-0.19 g; negative log molar value [pD(2)], 8.27+/-0.07 versus 7.92+/-0.08). When the KCl concentration was increased from 4.7 to 10 mmol/L in the bathing medium, no differences were observed in the contractile effect of Bay K 8644 between 2K1C and 2K (ME, 1.28+/-0.13 versus 1.14+/-0.21 g; pD(2), 8.56+/-0.08 versus 8.38+/-0.07). The cell resting membrane potential of 2K1C aorta vascular smooth muscle cells were less negative than in 2K (-35.19+/-4.91 versus -48.32+/-1.88 mV). Basal intracellular Ca(2+) concentration ([Ca(2+)](i)) was greater in cultured vascular smooth muscle cells from 2K1C than from 2K (293.4+/-25.83 versus 205.40+/-12.83 nmol/L). In 2K1C, Bay K 8644 induced a larger increase in [Ca(2+)](i) than in 2K (190.60+/-45.65 versus 92.57+/-14.67 nmol/L), and in 10 mmol/L KCl, this difference was abolished (134.90+/-45.12 versus 125.20+/-32.17 nmol/L). The main conclusion of the present work is that the increased contractile response to Bay K 8644 in 2K1C aortas is due to an increased Ca(2+) influx through voltage-gated Ca(2+) channels.

Impaired relaxation to acetylcholine in 2K-1C hypertensive rat aortas involves changes in membrane hyperpolarization instead of an abnormal contribution of endothelial factors

The contribution of endothelial factors and mechanisms underlying decreased acetylcholine-induced relaxation and endothelial inhibitory action on phenylephrine-induced contraction were evaluated in aortas of two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rats. Relaxation induced by acetylcholine in 2K-1C precontracted by phenylephrine was lower [Maximum Effect (ME): 71.33+/-3.36%; pD(2): 7.050+/-0.03] than in 2K (ME: 95.26+/-1.59%; pD(2): 7.31+/-0.07). This response was abolished by N(G)-nitro-L-arginine (L-NNA) in 2K-1C, but was only reduced in 2K (ME: 29.21+/-9.28%). Indomethacin had no effect in 2K-1C, and slightly attenuated acetylcholine-induced relaxation in 2K. The combination of L-NNA and indomethacin almost abolished acetylcholine-induced relaxation in 2K-1C, while in 2K, the inhibition (ME: 56.61+/-8.95%) was lower than the effect of L-NNA alone. During the KCl-induced precontraction, 2K and 2K-1C aortas showed similar acetylcholine-induced relaxation (43.50+/-5.64% vs. 41.60+/-4.36%), which was abolished by L-NNA. The levels of cGMP produced in response to acetylcholine were not different between 2K and 2K-1C. The sensitivity to sodium nitroprusside was lower in phenylephrine-precontracted aortas from 2K-1C than 2K, as showed by the pD(2) values (7.72+/-0.20 vs. 8.59+/-0.17), and this difference was abolished in aortas precontracted by KCl. The membrane potential was less negative in 2K-1C than in 2K (-41.57+/-1.19 vs. -51.00+/-1.13 mV) and hyperpolarization induced by acetylcholine was lower in 2K-1C than in 2K aortas (6.00+/-0.66 vs. 13.27+/-1.61 mV). Phenylephrine-induced contraction in aortas with endothelium was similar in both groups, and increased by the endothelium removal. This increase was lower in 2K-1C (from 1.32+/-0.06 to 1.90+/-0.21 g) than 2K (from 1.49+/-0.07 to 2.83+/-0.18 g). L-NNA and the endothelium removal had similar effect in 2K-1C (1.85+/-0.18 g) and were lower in 2K (2.18+/-0.20 g). Indomethacin decreased phenylephrine-induced contraction only in 2K. In conclusion, our major finding was a selective defect in smooth muscle membrane hyperpolarization, which could explain the decreased relaxation to acetylcholine and the attenuated inhibitory effect of endothelium on the contractile function in 2K-1C aortas.