The Role of Rho Kinase and Extracellular Regulated Kinase-Mitogen-Activated Protein Kinase in α2-Adrenoceptor-Mediated Vasoconstriction in the Porcine Palmar Lateral Vein

Vascular Functional Effect Mechanisms of Elabela in Rat Thoracic Aorta

BACKGROUND

Elabela is a recently discovered peptide hormone. The present study aims to investigate the vasorelaxant effect mechanisms of elabela in the rat thoracic aorta.

METHODS

The vascular rings obtained from the thoracic aortas of the male Wistar Albino rats were placed in the isolated tissue bath system. Resting tension was set to 1 gram. After the equilibration period, the vessel rings were contracted with phenylephrine or potassium chloride. Once a stable contraction was achieved, elabela-32 was applied cumulatively (10^-9 - 10^-6 molar) to the vascular rings. The experimental protocol was repeated in the presence of specific signaling pathway inhibitors or potassium channel blockers to determine the effect mechanisms of elabela.

RESULTS

Elabela showed a significant vasorelaxant effect in a concentration-dependent manner (p < 0.001). The vasorelaxant effect level of elabela was significantly reduced by the apelin receptor antagonist F13A, cyclooxygenase inhibitor indomethacin, adenosine monophosphate-activated protein kinase inhibitor dorsomorphin, protein kinase C inhibitor bisindolmaleimide, large-conductance calcium-activated potassium channel blocker iberiotoxin, and intermediate-conductance calcium-activated potassium channel blocker TRAM-34 (p < 0.001). However, the vasorelaxant effect level of elabela was not significantly affected by the endothelial nitric oxide synthase inhibitor nitro-L-arginine methyl ester and mitogen-activated protein kinase inhibitor U0126.

CONCLUSIONS

Elabela exhibits a prominent vasodilator effect in rat thoracic aorta. Apelin receptor, prostanoids, adenosine monophosphate-activated protein kinase, protein kinase C, and calcium-activated potassium channels are involved in the vasorelaxant effect mechanisms of elabela.

Fetal bovine serum promotes the development of in vitro porcine blastocysts by activating the Rho-associated kinase signalling pathway

Fetal bovine serum (FBS) supplementation has beneficial effects on invitro porcine embryonic development, but the underlying mechanisms are unclear. In the present study we found that the addition of FBS to PZM-3 increased the number of cells in porcine blastocysts and hatching rate invitro primarily by promoting proliferation of the inner cell mass and further differentiation. Moreover, based on the following results, we surmise that FBS benefits blastocyst development by activating Rho-associated kinase (ROCK) signalling: (1) the ROCK signalling inhibitor Y-27632 decreased the blastocyst rate and the number of cells in blastocysts, whereas FBS rescued the developmental failure induced by Y-27632; (2) the mRNA levels of two ROCK isoforms, ROCK1 and ROCK2, were significantly increased in blastocysts derived from medium containing FBS; and (3) FBS increased RhoA/Rho-kinase expression in the nucleus of embryonic cells. These results indicate that FBS promotes the invitro development of porcine embryos by activating ROCK signalling in a chemically defined medium.

Mitochondrial DNA: A new driver for sex differences in spontaneous hypertension

The prevalence of arterial hypertension (AH) is higher in men than in premenopausal women of the same age. AH has been characterized as a chronic inflammatory disease and activation of Toll-like receptors (TLR) by damage-associated molecular patterns (DAMPs) is involved. Mitochondrial DNA (mtDNA) may be released by end-organ damage, which is recognized and activates TLR9. The serum level of mtDNA is increased in AH. The aim of this study was to compare the serum mtDNA levels between male and female spontaneously hypertensive rats (SHR) and to evaluate the sex differences in the effect of mtDNA on the function, inflammation and signaling pathway related to TLR9 in the vasculature. Male and female 15-week-old SHR and Wistar rats were used to evaluate the arterial blood pressure, serum mtDNA, contractile response, inflammatory markers and signaling pathway related to TLR9. Male SHR had higher arterial blood pressure values and serum mtDNA compared to female SHR and to male and female normotensive Wistar rats. In male SHR aorta, mtDNA incubation increased the contractile response to phenylephrine, which was blunted by inhibition of TLR9, and also increased pro-inflammatory molecules IL-6 and TNF-α. However, in female SHR aorta, mtDNA incubation did not change the contractile response, reduced pro-inflammatory molecules and prevented oxidative stress. mtDNA incubation did not change the expression of TLR9, MyD88 and eNOS neither in male nor in female SHR aorta, but it increased the phosphorylation of ERK1/2 in male and reduced in female SHR aorta. The mtDNA differential modulation of vascular response in male and female SHR might contribute to sex differences in AH. This study contributes to the understanding of a need for more personalized therapeutic strategies for men and women with hypertension. Keywords: Sex differences, Arterial hypertension, Mitochondrial DNA, Toll-Like receptor 9.

Reduced blood pressure after smooth muscle EFNB2 deletion and the potential association of EFNB2 mutation with human hypertension risk

Ephrin B2 (EFNB2) is a ligand for erythropoietin-producing hepatocellular kinases (EPH), the largest family of receptor tyrosine kinases. It has critical functions in many biological systems, but is not known to regulate blood pressure. We generated mice with a smooth muscle cell (SMC)-specific deletion of EFNB2 and investigated its roles in blood pressure regulation and vascular SMC (VSMC) contractility. Male Efnb2 knockout (KO) mice presented reduced blood pressure, whereas female KO mice had no such reduction. Both forward signaling from EFNB2 to EPHs and reverse signaling from EPHs to EFNB2 were involved in regulating VSMC contractility, with EPHB4 serving as a critical molecule for forward signaling, based on crosslinking studies. We also found that a region from aa 313 to aa 331 in the intracellular tail of EFNB2 was essential for reverse signaling regulating VSMC contractility, based on deletion mutation studies. In a human genetic study, we identified five SNPs in the 3' region of the EFNB2 gene, which were in linkage disequilibrium and were significantly associated with hypertension for male but not female subjects, consistent with our findings in mice. The coding (minor) alleles of these five SNPs were protective in males. We have thus discovered a previously unknown blood pressure-lowering mechanism mediated by EFNB2 and identified EFNB2 as a gene associated with hypertension risk in humans.

Protective Effect of Dermal Brimonidine Applications Against UV Radiation-induced Skin Tumors, Epidermal Hyperplasia and Cell Proliferation in the Skin of Hairless Mice

Brimonidine at 0.18%, 1% and 2% concentrations applied topically in hairless mice significantly decreased tumor burden and incidences of erythema, flaking, wrinkling and skin thickening induced by UVR. The unbiased median week to tumor ≥1 mm was increased by the 1% and 2% concentrations. The tumor yield was reduced by all concentrations at week 40 for all tumor sizes but the ≥4 mm tumors with the 0.18% concentration. At week 52, the tumor yield was reduced for all tumor sizes and all brimonidine concentrations. The tumor incidence was reduced by all concentrations at week 40 for all tumor sizes, but the ≥4 mm tumor with the 0.18% concentration and at week 52 for all tumor sizes with the 1% and 2% concentrations and with the 0.18% concentration only for the ≥4 mm tumors. Reductions in ≥4 mm tumor incidences compared to the vehicle control group were 54%, 91% and 86% by week 52 for the 0.18%, 1% and 2% concentrations, respectively. Brimonidine at 2% applied 1 h before or just after UVB irradiation on hairless mice decreased epidermal hyperplasia by 23% and 32% and epithelial cell proliferation by 59% and 64%, respectively, similar to an epidermal growth factor receptor (EGFR) inhibitor.

Distinct roles of ROCK1 and ROCK2 during development of porcine preimplantation embryos

Cell-to-cell contact mediated by cell adhesion is fundamental to the compaction process that ensures blastocyst quality during embryonic development. In this study, we first showed that Rho-associated coiled-coil protein kinases (ROCK1 and ROCK2) were expressed both in porcine oocytes and IVF preimplantation embryos, playing different roles in oocytes maturation and embryo development. The amount of mRNA encoding ROCK1 and the protein concentration clearly increased between the eight-cell and morula stages, but decreased significantly when blastocysts were formed. Conversely, ROCK2 was more abundant in the blastocyst compared with other embryonic stages. Moreover, immunostaining showed that ROCK1 protein distribution changed as the embryo progressed through cleavage and compaction to the morula stage. Initially, the protein was predominantly associated with the plasma membrane but later became cytoplasmic. By contrast, ROCK2 protein was localized in both the cytoplasm and the spindle rotation region during oocyte meiosis, but in the cytoplasm and nucleus as the embryo developed. In addition, ROCK2 was present in the trophectoderm cells of the blastocyst. Treatment with 15 μM Y27632, a specific inhibitor of ROCKs, completely blocked further development of early four-cell stage embryos. Moreover, we did not detect the expression ofROCK1but did detectROCK2expression in blastocysts. Moreover, lysophosphatidic acid an activator of ROCKs significantly improved the rates of blastocyst formation. These data demonstrate that ROCKs are required for embryo development to the blastocyst stage. Together, our results indicate that ROCK1 and ROCK2 may exert different biological functions during the regulation of compaction and in ensuring development of porcine preimplantation embryos to the blastocyst stage.

Dexamethasone induces rapid promotion of norepinephrine‑mediated vascular smooth muscle cell contraction

The aim of the present study was to identify the rapid effect of dexamethasone (Dex) on norepinephrine (NE)‑mediated contraction of vascular smooth muscle cells (VSMCs) and to establish the underlying mechanism(s). Rat VSMCs were preincubated with lipopolysaccharide to simulate acute septic shock. Myosin light chain (MLC20) phosphorylation of VSMCs was detected by western blot analysis to observe the effects of Dex on NE‑mediated contraction. Activation of the RhoA/ RhoA kinase (ROCK), extracellular signal‑regulated kinase (ERK) and p38 signaling pathways was detected by western blot analysis to explore the mechanism. It was identified that Dex rapidly promoted NE‑induced phosphorylation of MLC20 in VSMCs and this effect may be non‑genomic. The RhoA/ROCK, ERK and p38 pathways were demonstrated to be important for the rapid effect of Dex‑induced promotion of NE‑mediated contraction in VSMCs. The present results indicate that Dex may rapidly reverse the hyporeactivity of vasoconstriction to NE in vitro and this effect may be mediated by specific non‑genomic mechanisms through increased activation of the RhoA/ROCK, ERK and p38 signaling pathways.

The extracellular signal-regulated kinase (ERK) pathway: a potential therapeutic target in hypertension

Hypertension is a risk factor for myocardial infarction, stroke, renal failure, heart failure, and peripheral vascular disease. One feature of hypertension is a hyperresponsiveness to contractile agents, and inhibition of vasoconstriction forms the basis of some of the treatments for hypertension. Hypertension is also associated with an increase in the growth and proliferation of vascular smooth muscle cells, which can lead to a thickening of the smooth muscle layer of the blood vessels and a reduction in lumen diameter. Targeting both the enhanced contractile responses, and the increased vascular smooth muscle cell growth could potentially be important pharmacological treatment of hypertension. Extracellular signal-regulated kinase (ERK) is a member of the mitogen-activated protein kinase family that is involved in both vasoconstriction and vascular smooth muscle cell growth and this, therefore, makes it attractive therapeutic target for treatment of hypertension. ERK activity is raised in vascular smooth muscle cells from animal models of hypertension, and inhibition of ERK activation reduces both vascular smooth muscle cell growth and vasoconstriction. This review discusses the potential for targeting ERK activity in the treatment of hypertension.

Simvastatin evokes an unpredicted inhibition of β-adrenoceptor-mediated vasodilatation in porcine coronary artery

HMG-CoA reductase inhibitors, or statins, are widely used as cholesterol-lowering agents in the treatment of dyslipidemias. Statins have also been reported to have pleiotropic effects, independent of their effects on cholesterol synthesis, possibly through inhibition of the monomeric G proteins Ras and Rho, which are able to signal through ERK and Rho kinase activities, respectively. We have previously demonstrated that inhibition of ERK activation enhances β-adrenoceptor-mediated vasodilatation in the porcine isolated coronary artery. As statins can also inhibit ERK activation, the initial aim of this study was to determine whether statins have a similar influence on β-adrenoceptor-evoked vasodilatation. Segments of porcine distal coronary artery were mounted in a Mulvany wire myograph and bathed in Krebs-Henseleit buffer gassed with 95% O(2)/5% CO(2) and maintained at 37 °C. Tissues were pre-contracted with the thromboxane mimetic U46619 prior to cumulative concentration-response curves to the β-adrenoceptor agonist salbutamol in the absence or presence of simvastatin (1, 5 or 10 μM), pravastatin (10 μM), or lovastatin (10 μM). Simvastatin inhibited the salbutamol-induced relaxation of the coronary artery. Similar effects were seen with lovastatin, but not pravastatin or the sodium salt of simvastatin. Simvastatin, but not pravastatin also inhibited the relaxations to the Ca(2+)-activated K(+) channel opener NS1619 and the K(ATP) channel opener pinacidil. Unexpectedly, these data indicate that, rather than enhancing β-adrenoceptor-mediated vasodilatation, lipophilic statins impair these responses. This is likely to be due to effects on K(+) channels.

Pre-contraction with the thromboxane-mimetic U46619 enhances P2X receptor-mediated contractions in isolated porcine splenic artery

We have previously demonstrated that the thromboxane-mimetic U46619 enhances α(2)-adrenoceptor-mediated contractions through increased activation of extracellular signal-regulated kinase (ERK). In this study, we determined whether U46619 also enhances P2X-mediated contractions through the same pathway. Segments of porcine splenic artery were mounted in isolated tissue baths. Tissues were pre-contracted with U46619 to 10-20% of the response to 60 mM KCl prior to addition of α,β-methylene ATP (P2X receptor agonist). The effect of inhibition of ERK activation with the mitogen-activated protein (MAP)/ERK kinase inhibitor PD98059 (50 μM), Rho kinase inhibition with Y27632 (10 μM), p38 MAP kinase with SB203580 (10 μM) or L-type calcium channels with nifedipine (1 μM) on both the direct and enhanced contractions was then determined. U46619 enhanced the contractions to α,β-methylene ATP. Although PD98059 inhibited the direct contractions to α,β-methylene ATP, it had no effect on the U46619-enhanced contractions. Similarly, Y27632 and SB203580 inhibited the direct contractions to α,β-methylene ATP, but had no effect on the enhanced contractions. Nifedipine inhibited the responses to α,β-methylene ATP in the absence and presence of U46619. This study demonstrates that pre-contraction with U46619 enhances P2X-mediated contractions in the porcine splenic artery through a mechanism independent of ERK, Rho kinase and p38 MAP kinase. Further studies are required to determine the exact mechanism involved.

The heme oxygenase-1 protein is overexpressed in human renal cancer cells following activation of the Ras-Raf-ERK pathway and mediates anti-apoptotic signal

The stress-inducible cytoprotective enzyme heme oxygenase-1 (HO-1) may play a critical role in the growth and metastasis of tumors. We demonstrated that overexpressed HO-1 promotes the survival of renal cancer cells by inhibiting cellular apoptosis; we also showed that the proto-oncogene H-Ras becomes activated in these cells under stress following treatment with immunosuppressive agents. However, it is not known if there is an association between Ras activation and HO-1 overexpression. Here, we examined if the activation of H-Ras pathway could induce HO-1, and promote the survival of renal cancer cells (786-0 and Caki-1). In co-transfection assays, using HO-1 promoter-luciferase construct, we found that the activated H-Ras, H-Ras(12V), promoted HO-1 transcriptional activation. The inhibition of endogenous H-Ras by specific dominant-negative mutant/siRNA markedly ablated the HO-1 promoter activity. Active H-Ras increased HO-1 mRNA and protein expression. Moreover, transfection with effector domain mutant constructs of active H-Ras showed that H-Ras-induced HO-1 overexpression was primarily mediated through the Raf signaling pathway. Using pharmacological inhibitor, we observed that ERK is a critical intermediary molecule for Ras-Raf-induced HO-1 expression. Activation of H-Ras and ERK promoted nuclear translocation of the transcription factor Nrf2 for its binding to the specific sequence of HO-1 promoter. The knockdown of Nrf2 significantly inhibited H-Ras-induced HO-1 transcription. Finally, by FACS analysis using Annexin-V staining, we demonstrated that the H-Ras-ERK-induced and HO-1-mediated pathway could protect renal cancer cells from apoptosis. Thus, targeting the Ras-Raf-ERK pathway for HO-1 overexpression may serve as novel therapeutics for the treatment of renal cancer.

Renal and vascular benefits of C-peptide: Molecular mechanisms of C-peptide action

C-peptide has long been thought to be an inert byproduct of insulin production, but it has become apparent, and accepted, that C-peptide has important biological properties. C-peptide displays beneficial effects in many tissues affected by diabetic complications, such as increased peripheral blood flow and protection from renal damage. However, the mechanisms mediating these effects remain unclear. C-peptide interacts with cellular membranes at unidentified sites distinctive of the insulin family of receptors, and signals to multiple targets known to play a role in diabetes and diabetic complications, such as Na⁺/K⁺-ATPase and NOS. In general, the physiological and molecular effects of C-peptide resemble insulin, but C-peptide also possesses traits separate from those of insulin. These basic studies have been confirmed in human studies, suggesting that C-peptide may lend itself to clinical applications. However, the molecular and physiological properties of C-peptide are not completely elucidated, and large clinical studies have not begun. In order to further these goals, we critically summarize the current state of knowledge regarding C-peptide’s renal and vascular effects and the molecular signaling of C-peptide.

Rho kinase activation and ROS production contributes to the cooling enhanced contraction in cutaneous equine digital veins

A decrease in environmental temperature can directly affect the contractility of cutaneous vasculature, mediated in part by α2-adrenoceptors. Most of the cellular mechanisms underlying the cooling-enhanced contractility to α2-adrenoceptor agonists have been reported in cutaneous arteries but little information is available on cutaneous veins. To investigate the cellular mechanisms associated with the cooling-enhanced contraction to UK-14304 (α2-adrenoceptor agonist), isolated equine digital veins (EDVs) were studied at 30°C and 22°C. The effects of inhibitors were studied on the contractile response to UK-14304 (0.1 μM). The cooling-enhanced responses were inhibited by Rho kinase inhibitors [maximum response to UK-14304 95.2 ± 8% of response to depolarizing Krebs solution (DKS) in control vessels cooled to 22°C, compared with 31.4 ± 6% in the presence of fasudil 1 μM and 75.8 ± 6% with Y-27632 0.1 μM] and the effects of these inhibitors were considerably less at 30°C (control response 56.4 ± 5% of DKS; 34.9 ± 6% with fasudil 1 μM and 50.6 ± 9% with Y-27632 0.1 μM). Furthermore, Western blotting showed that one of the downstream targets for Rho kinase activity, ezrin/radixin/moesin, was phosphorylated after cooling and reduced by fasudil (1 μM) only at 22°C. The activation of protein kinase C contributed to the contractile response, but predominantly at 30°C (maximum response 82.3 ± 9% of DKS for control; 57.7 ± 10% in the presence of chelerythrine 10 μM) with no significant effect at 22°C. The reduction of the response at 22°C by antioxidants, rotenone (14% reduction), and tempol (21% reduction) suggested the contribution of reactive oxygen species (ROS). No evidence was obtained to support the participation of tyrosine kinase. These data demonstrate that Rho kinase activation and the production of ROS contributes to the cooling-enhanced contraction in these cutaneous digital veins.

Extracellular signal-regulated kinase and phosphatidylinositol-3-kinase/AKT signalling pathways in the human carotid body and peripheral ganglia

Extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K)/AKT signalling pathways are involved in various cell functions, but their developmental regulation in the carotid body and peripheral ganglia has not yet been fully investigated. ERK and AKT immunolocalisation and activation were studied by anti-ERK, -pERK, -AKT and -pAKT immunohistochemistry in carotid bodies and peripheral (sympathetic and sensory) ganglia, sampled at autopsy from 4 foetuses (mean gestational age 177 days), 8 infants (mean age 10 months), 8 young adults (mean age 38 years) and 6 aged adults (mean age 72.4 years). ERK and AKT immunopositivity and activation were demonstrated in both glomic type I cells and peripheral ganglionic cells and are ascribed to local action by neuromodulators or neurotrophic factors. Mean percentages of ERK- and pERK-immunopositive glomic type I cells were lower in foetuses than in infants and young adults, and those of AKT-immunopositive glomic type I cells were lower in foetuses than in young and old adults, suggesting incomplete maturation of these two signalling pathways in foetal life. Both pERK and pAKT immunoreactions were detected only in post-natal sympathetic and sensory ganglia, demonstrating that, also in peripheral ganglia, these pathways are not yet fully operative during the foetal stage.

Pharmacological characterization of SAR407899, a novel rho-kinase inhibitor

Recent advances in basic and clinical research have identified Rho kinase as an important target potentially implicated in a variety of cardiovascular diseases. Rho kinase is a downstream mediator of RhoA that leads to stress fiber formation, membrane ruffling, smooth muscle contraction, and cell motility. Increased Rho-kinase activity is associated with vasoconstriction and elevated blood pressure. We identified a novel inhibitor of Rho kinase (SAR407899) and characterized its effects in biochemical, cellular, tissue-based, and in vivo assays. SAR407899 is an ATP-competitive Rho-kinase inhibitor, equipotent against human and rat-derived Rho-kinase 2 with inhibition constant values of 36 nM and 41 nM, respectively. It is highly selective in panel of 117 receptor and enzyme targets. SAR407899 is approximately 8-fold more active than fasudil. In vitro, SAR407899 demonstrated concentration-dependent inhibition of Rho-kinase-mediated phosphorylation of myosin phosphatase, thrombin-induced stress fiber formation, platelet-derived growth factor-induced proliferation, and monocyte chemotactic protein-1-stimulated chemotaxis. SAR407899 potently (mean IC(50) values: 122 to 280 nM) and species-independently relaxed precontracted isolated arteries of different species and different vascular beds. In vivo, over the dose range 3 to 30 mg/kg PO, SAR407899 lowered blood pressure in a variety of rodent models of arterial hypertension. The antihypertensive effect of SAR407899 was superior to that of fasudil and Y-27632. In conclusion, SAR407899 is a novel and potent selective Rho-kinase inhibitor with promising antihypertensive activity.

Proinsulin C-peptide constricts glomerular afferent arterioles in diabetic mice. A potential renoprotective mechanism

OBJECTIVE

an increased glomerular filtration rate (GFR) has been postulated as a potential mechanism involved in the progression of diabetic nephropathy. Studies suggest that C-peptide exerts a renoprotective effect on diabetes. The peptide decreases hyperfiltration in patients with type 1 diabetes, as well as in diabetic animal models. In this study, we investigated whether C-peptide causes a change in arteriolar diameter.

RESEARCH DESIGN AND METHODS

C57-Bl mice were made diabetic by means of a single intravenous injection of alloxan 2 wk prior to the experiment. Age-matched normoglycemic mice served as controls. Afferent arterioles, intact with the glomeruli, were dissected and microperfused. The effect of luminal application of C-peptide, compared with scrambled C-peptide or vehicle, was investigated. The effect of the Rho-kinase inhibitor Y-27632 was also investigated.

RESULTS

C-peptide constricted afferent arterioles in diabetic mice by -27% compared with the control value. Normoglycemic arterioles administered C-peptide displayed a delayed and minute response (-4%). Scrambled C-peptide or vehicle administration, whether administered to hyperglycemic or normoglycemic mice, did not induce any effect. Addition of Y-27632 abolished the effect of C-peptide.

CONCLUSION

C-peptide induces constriction of afferent arterioles in diabetic mice. This can reduce enhanced GFR and may be one of the mechanisms in the renoprotective action of C-peptide in diabetes.

Angiotensin II Activates Extracellular Signal-Regulated Kinase Independently of Receptor Tyrosine Kinases in Renal Smooth Muscle Cells: Implications for Blood Pressure Regulation

Angiotensin II can cause hypertension through enhanced vasoconstriction of renal vasculature. One proposed mechanism for reduction of angiotensin II-induced hypertension is through inhibition of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase cascade. MEK/ERK has been shown to phosphorylate the regulatory subunit of myosin light chain at identical positions as myosin light chain kinase. There are multiple mechanisms proposed regarding angiotensin II-mediated ERK activation. We hypothesized that renal microvascular smooth muscle cells (RmuVSMCs) signal through a unique pathway compared with thoracic aorta smooth muscle cells (TASMCs), which is involved in blood pressure regulation. Use of epidermal growth factor (EGF) and platelet derived growth factor (PDGF) receptor-specific inhibitors 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478) and 6,7-dimethoxy-3-phenylquinoxaline (AG1296), respectively, demonstrates that angiotensin II activates ERK in TASMCs, but not RmuVSMCs, through transactivation of EGF and PDGF receptors. In addition, inhibition of Src with its specific inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine (PP2) abolishes angiotensin II-, but not EGF-or PDGF-, mediated phosphorylation of ERK in RmuVSMCs, yet it has no effect in TASMCs. The physiological significance of transactivation was examined in vivo using anesthetized Wistar-Kyoto rats with 15 mg/kg 2'-amino-3'-methoxyflavone (PD98059), an MEK inhibitor, as well as 20 mg/kg AG1478 and 1.5 mg/kg AG1296 in an acute model of angiotensin II-mediated increase in blood pressure. None of the inhibitors had an effect on basal blood pressure, and only PD98059 reduced angiotensin II-mediated increase in blood pressure. Moreover, in RmuVSMCs, but not TASMCs, angiotensin II localizes phosphorylated ERK to actin filaments. In conclusion, angiotensin II signals through a unique mechanism in the renal vascular bed that may contribute to hypertension.

Role of alpha2C-adrenoceptors in the reduction of skin blood flow induced by local cooling in mice

BACKGROUND AND PURPOSE

The reduction of skin blood flow induced by local cooling results from a reflex increase in sympathetic output and an enhanced vasoconstrictor activity of cutaneous vessels. The present study investigated the latter local response in vivo in tetrodotoxin-treated mice, in which the sympathetic nerve tone was abolished.

EXPERIMENTAL APPROACH

Male ddY mice, anaesthetized with pentobarbitone, were treated with tetrodotoxin and artificially ventilated. The plantar skin blood flow (PSBF) was measured by laser Doppler flowmetry.

KEY RESULTS

Cooling the air temperature around the left foot from 25 to 10 degrees C decreased the PSBF of the left foot. Bunazosin, an alpha (1)-adrenoceptor antagonist, RS79948, an alpha (2)-adrenoceptor antagonist, and MK-912, an alpha (2C)-adrenoceptor antagonist, all significantly inhibited the cooling-induced reduction of PSBF; the inhibition by bunazosin was relatively small compared with that by RS79948 and MK-912. The response was not affected by guanethidine or bretylium, but was diminished in adrenalectomized mice. An intra-arterial injection of clonidine, an alpha (2)-adrenoceptor agonist, to the left iliac artery of adrenalectomized mice caused a transient decrease in PSBF, which was significantly augmented at 10 degrees C. MK-912 suppressed only the augmented portion at 10 degrees C. Y-27632, H-1152 and fasudil, Rho kinase inhibitors, also inhibited the cooling-induced reduction of PSBF. RS79948 caused no further reduction of the cooling-induced response after the inhibition by Y-27632.

CONCLUSIONS AND IMPLICATIONS

Local cooling-induced reduction of skin blood flow in mice primarily results from increased reactivity of alpha (2C)-adrenoceptors to circulating catecholamines, in which the Rho/Rho kinase pathway is involved.

Cooling augments vasoconstriction mediated by 5-HT1 and alpha2-adrenoceptors in the isolated equine digital vein: involvement of Rho kinase

The vasculature of the equine digit fulfils an important role in thermoregulation. In other species, it has been found that cooling may enhance the response of cutaneous vessels to 5-hydroxytryptamine (5-HT) and alpha(2)-adrenoceptor agonists. Translocation of alpha(2)-adrenoceptors to the smooth muscle cell membrane, mediated by Rho kinase, is thought to be involved in the cooling-enhanced response in mouse tail arteries. However, little is known about the effect of cooling on 5-HT receptor function. The present investigation compared the response of 5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline (UK14304:1 nM to 30 microM), methoxamine (0.1 nM to 30 microM; in the presence of yohimbine 0.1 microM), 5-carboxamidotryptamine (5-CT; 0.1 nM to 10 microM) and alpha-methyl 5-HT (0.1 nM to 10 microM) in the isolated equine digital vein at 30 degrees C and 22 degrees C. The effect of the Rho kinase inhibitor, fasudil (1 microM), and the recovery of the response after the irreversible blockade of surface receptors with phenoxybenzamine (10 microM) or 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ;10 microM), was established. Moderate cooling significantly increased the maximum response to alpha-methyl 5-HT, 5-CT and UK14304 and shifted their response curves to the left. Cooling also augmented the phenoxybenzamine- and EEDQ-resistant response to UK14304 and 5-CT, respectively. Fasudil had no effect on the contractile response at 30 degrees C, but completely abrogated the effect of cooling on the response to 5-CT and UK14304. The response to methoxamine was not significantly affected by cooling. These results suggest that Rho kinase plays an important role in the cooling-enhanced response mediated by 5-HT(1B/D) receptors and alpha(2)-adrenoceptors. The exact mechanism by which Rho/Rho kinase enhances the functional responses mediated by these receptors in these vessels has yet to be determined.

Mechanisms underlying lysophosphatidylcholine-induced potentiation of vascular contractions in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat aorta

BACKGROUND AND PURPOSE

The effect of lysophosphatidylcholine (LPC) on aortic contractions in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 diabetic model, was studied.

EXPERIMENTAL APPROACH

Using OLETF rats and control (Long Evans Tokushima Otsuka (LETO)) rats, the effects of LPC on the contractions induced by high-K(+) (10-40 mM), UK14,304 (10 approximately 100 nM; a selective alpha(2)-adrenoceptor agonist) and sodium orthovanadate (SOV; 10 microM approximately 3 mM) in endothelium-denuded aortae were compared. Aortic ERK activity and the mRNA expression for GPR4 (a putative LPC receptor) were also measured.

KEY RESULTS

OLETF rats exhibited (vs. age-matched LETO rats): (1) greater potentiation of high-K(+)-induced contraction by 10 microM LPC - a potentiation attenuated by 10 microM genistein, protein tyrosine kinase (PTK) inhibitor, (2) greater potentiation of UK14,304 (10 approximately 100 nM)-induced contractions by LPC (1 microM approximately 10 microM) - a potentiation attenuated by 10 microM genistein, 50 microM tyrphostin A23 (PTK inhibitor) or 10 microM PD98059 (MEK 1/2 inhibitor), (3) greater basal and LPC (1 microM)-induced ERK activities, (4) greater basal and 100 nM UK14,304-stimulated ERK2 activities in both the absence and presence of 10 microM LPC, (5) greater SOV (10 microM approximately 3 mM)-induced contractions, (6) greater potentiation of SOV-induced contractions by 10 microM LPC - a potentiation suppressed by 10 microM PD98059 or 10 microM genistein, (7) upregulation of GPR4 mRNA.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the LPC-induced potentiation of contractions in the OLETF rat aorta may be attributable to increased PTKs or ERK activity and/or to receptor upregulation.

Rho kinase inhibitors reduce neurally evoked contraction of the rat tail artery in vitro

The effects of Rho kinase inhibitors (Y27632, HA-1077) on contractions to electrical stimulation and to application of phenylephrine, clonidine or alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-mATP) were investigated in rat tail artery in vitro. In addition, continuous amperometry and intracellular recording were used to monitor the effects of Y27632 on noradrenaline (NA) release and postjunctional electrical activity, respectively. Y27632 (0.5 and 1 microM) and HA-1077 (5 microM) reduced neurally evoked contractions. In contrast, the protein kinase C inhibitor, Ro31-8220 (1 microM), had little effect on neurally evoked contraction. In the absence and the presence of Y27632 (0.5 microM), the reduction of neurally evoked contraction produced by the alpha-adrenoceptor antagonists prazosin (10 nM) and idazoxan (0.1 microM) was similar. The P2-purinoceptor antagonist, suramin (0.1 mM), had no inhibitory effect on neurally evoked contraction in the absence or the presence of Y27632 (1 microM). In the presence of Y27632, desensitization of P2X-purinoceptors with alpha,beta-mATP (10 microM) increased neurally evoked contractions.Y27632 (1 microM) and H-1077 (5 microM) reduced sensitivity to phenylephrine and clonidine. In addition, Y27632 reduced contractions to alpha,beta-mATP (10 microM). Y27632 (1 microM) had no effect on the NA-induced oxidation currents or the purinergic excitatory junction potentials and NA-induced slow depolarizations evoked by electrical stimulation. Rho kinase inhibitors reduce sympathetic nerve-mediated contractions of the tail artery. This effect is mediated at a postjunctional site, most likely by inhibition of Rho kinase-mediated 'Ca2+ sensitization' of the contractile apparatus.

Pollutant particles produce vasoconstriction and enhance MAPK signaling via angiotensin type I receptor

Exposure to particulate matter (PM) is associated with acute cardiovascular mortality and morbidity, but the mechanisms are not entirely clear. In this study, we hypothesized that PM may activate the angiotensin type 1 receptor (AT1R), a G protein-coupled receptor that regulates inflammation and vascular function. We investigated the acute effects of St. Louis, Missouri, urban particles (UPs; Standard Reference Material 1648) on the constriction of isolated rat pulmonary artery rings and the activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 mitogen-activated protein kinases (MAPKs) in human pulmonary artery endothelial cells with or without losartan, an antagonist of AT1R. UPs at 1-100 microg/mL induced acute vasoconstriction in pulmonary artery. UPs also produced a time- and dose-dependent increase in phosphorylation of ERK1/2 and p38 MAPK. Losartan pretreatment inhibited both the vasoconstriction and the activation of ERK1/2 and p38. The water-soluble fraction of UPs was sufficient for inducing ERK1/2 and p38 phosphorylation, which was also losartan inhibitable. Copper and vanadium, two soluble transition metals contained in UPs, induced pulmonary vasoconstriction and phosphorylation of ERK1/2 and p38, but only the phosphorylation of p38 was inhibited by losartan. The UP-induced activation of ERK1/2 and p38 was attenuated by captopril, an angiotensin-converting enzyme inhibitor. These results indicate that activation of the local renin-angiotensin system may play an important role in cardiovascular effects induced by PM.