Role of calcium influx and intracellular calcium stores in angiotensin II-mediated calcium hyper-responsiveness in smooth muscle from spontaneously hypertensive rats

7-Hydroxycoumarin Induces Vasorelaxation in Animals with Essential Hypertension: Focus on Potassium Channels and Intracellular Ca2+ Mobilization

Cardiovascular diseases (CVD) are the deadliest noncommunicable disease worldwide. Hypertension is the most prevalent risk factor for the development of CVD. Although there is a wide range of antihypertensive drugs, there still remains a lack of blood pressure control options for hypertensive patients. Additionally, natural products remain crucial to the design of new drugs. The natural product 7-hydroxycoumarin (7-HC) exhibits pharmacological properties linked to antihypertensive mechanisms of action. This study aimed to evaluate the vascular effects of 7-HC in an experimental model of essential hypertension. The isometric tension measurements assessed the relaxant effect induced by 7-HC (0.001 μM–300 μM) in superior mesenteric arteries isolated from hypertensive rats (SHR, 200–300 g). Our results suggest that the relaxant effect induced by 7-HC rely on K⁺-channels (K_ATP, BK_Ca, and, to a lesser extent, K_v) activation and also on Ca²⁺ influx from sarcolemma and sarcoplasmic reticulum mobilization (inositol 1,4,5-triphosphate (IP3) and ryanodine receptors). Moreover, 7-HC diminishes the mesenteric artery’s responsiveness to α1-adrenergic agonist challenge and improves the actions of the muscarinic agonist and NO donor. The present work demonstrated that the relaxant mechanism of 7-HC in SHR involves endothelium-independent vasorelaxant factors. Additionally, 7-HC reduced vasoconstriction of the sympathetic agonist while improving vascular endothelium-dependent and independent relaxation.

How Structure, Mechanics, and Function of the Vasculature Contribute to Blood Pressure Elevation in Hypertension

Large conduit arteries and the microcirculation participate in the mechanisms of elevation of blood pressure (BP). Large vessels play roles predominantly in older subjects, with stiffening progressing after middle age leading to increases in systolic BP found in most humans with aging. Systolic BP elevation and increased pulsatility penetrate deeper into the distal vasculature, leading to microcirculatory injury, remodelling, and associated endothelial dysfunction. The result is target organ damage in the heart, brain, and kidney. In younger individuals genetically predisposed to high BP, increased salt intake or other exogenous or endogenous risk factors for hypertension, including overweight and excess alcohol intake, lead to enhanced sympathetic activity and vasoconstriction. Enhanced vasoconstrictor responses and myogenic tone become persistent when embedded in an increased extracellular matrix, resulting in remodelling of resistance arteries with a narrowed lumen and increased media-lumen ratio. Stimulation of the renin-angiotensin-aldosterone and endothelin systems and inflammatory and immune activation, to which gut microbiome dysbiosis may contribute as a result of salt intake, also participate in the injury and remodelling of the microcirculation and endothelial dysfunction. Inflammation of perivascular fat and loss of anticontractile factors play roles as well in microvessel remodelling. Exaggerated myogenic tone leads to closure of terminal arterioles, collapse of capillaries and venules, functional rarefaction, and eventually to anatomic rarefaction, compromising tissue perfusion. The remodelling of the microcirculation raises resistance to flow, and accordingly raises BP in a feedback process that over years results in stiffening of conduit arteries and systo-diastolic or predominantly systolic hypertension and, more rarely, predominantly diastolic hypertension. Thus, at different stages of life and the evolution of hypertension, large vessels and the microcirculation interact to contribute to BP elevation.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Interactions between renal vascular resistance and endothelium-derived hyperpolarization in hypertensive rats in vivo

Endothelium derived signaling mechanisms play an important role in regulating vascular tone and endothelial dysfunction is often found in hypertension. Endothelium-derived hyperpolarization (EDH) plays a significant role in smaller renal arteries and arterioles, but its significance in vivo in hypertension is unresolved. The aim of this study was to characterize the EDH-induced renal vasodilation in normotensive and hypertensive rats during acute intrarenal infusion of ACh. Our hypothesis was that the increased renal vascular resistance (RVR) found early in hypertension would significantly correlate with reduced EDH-induced vasodilation. In isoflurane-anesthetized 12-week-old normo- and hypertensive rats blood pressure and renal blood flow (RBF) was measured continuously. RBF responses to acute intrarenal ACh infusions were measured before and after inhibition of NO and prostacyclin. Additionally, RVR was decreased or increased using inhibition or activation of adrenergic receptors or by use of papaverine and angiotensin II. Intrarenal infusion of ACh elicited a larger increase in RBF in hypertensive rats compared to normotensive rats suggesting that endothelial dysfunction is not present in 12-week-old hypertensive rats. The EDH-induced renal vasodilation (after inhibition of NO and prostacyclin) was similar between normo- and hypertensive rats. Reducing RVR by inhibition of α1 -adrenergic receptors significantly increased the renal EDH response in hypertensive rats, but a similar increase was found after activating α-adrenergic receptors using norepinephrine. The results show that renal EDH is present and functional in 12-week-old normo- and hypertensive rats. Interestingly, both activation and inactivation of α1 -adrenergic receptors elicited an increase in the renal EDH-induced vasodilation.

Effect of Cyclosporin A and Angiotensin II on cytosolic calcium levels in primary human gingival fibroblasts

Background:

To evaluate the effect of Cyclosporin A (CsA) and angiotensin II (Ang II) on cytosolic calcium levels in cultured human gingival fibroblasts (HGFs).

Materials and Methods:

Healthy gingival samples from six volunteers were obtained, and primary HGFs were cultured. Cell viability and proliferation assay were performed to identify the ideal concentrations of CsA and Ang II. Cytosolic calcium levels in cultured gingival fibroblasts treated with CsA and Ang II were studied using colorimetric assay, confocal and fluorescence imaging. Statistical analyses were done using SPSS software and GraphPad Prism.

Results:

Higher levels of cytosolic levels were evident in cells treated with CsA and Ang II when compared to control group and was statistically significant (P < 0.05) in both colorimetric assay and confocal imaging. Fluorescent images of the cultured HGFs revealed the same.

Conclusion:

Thus calcium being a key player in major cellular functions, plays a major role in the pathogenesis of drug-induced gingival overgrowth.

Angiotensin II and vascular injury

Vascular injury, characterized by endothelial dysfunction, structural remodelling, inflammation and fibrosis, plays an important role in cardiovascular diseases. Cellular processes underlying this include altered vascular smooth muscle cell (VSMC) growth/apoptosis, fibrosis, increased contractility and vascular calcification. Associated with these events is VSMC differentiation and phenotypic switching from a contractile to a proliferative/secretory phenotype. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Among the many factors involved in vascular injury is Ang II. Ang II, previously thought to be the sole biologically active downstream peptide of the renin-angiotensin system (RAS), is converted to smaller peptides, [Ang III, Ang IV, Ang-(1-7)], that are functional and that modulate vascular tone and structure. The actions of Ang II are mediated via signalling pathways activated upon binding to AT1R and AT2R. AT1R activation induces effects through PLC-IP3-DAG, MAP kinases, tyrosine kinases, tyrosine phosphatases and RhoA/Rho kinase. Ang II elicits many of its (patho)physiological actions by stimulating reactive oxygen species (ROS) generation through activation of vascular NAD(P)H oxidase (Nox). ROS in turn influence redox-sensitive signalling molecules. Here we discuss the role of Ang II in vascular injury, focusing on molecular mechanisms and cellular processes. Implications in vascular remodelling, inflammation, calcification and atherosclerosis are highlighted.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.

Upregulated TRPC3 and Downregulated TRPC1 Channel Expression during Hypertension is Associated with Increased Vascular Contractility in Rat

Transient receptor potential (TRP) C1 and C3 (TRPC1 and TRPC3) are expressed in vascular smooth muscle cells and are thought to be involved in vascular contractility. In the present study, we determined the effect of systemic hypertension on TRPC1/TRPC3 channel expression and vascular contractility in rat carotid artery (CA). CA were studied from male spontaneously hypertensive rats (SHR), Wistar-Kyoto (WKY), and Long Evans (LE) rats. TRPC1/3 expression was determined by RT-PCR and Western blot. TRP channel function was evaluated by whole-cell patch clamp, using UTP (60 μM) to stimulate TRPC1/3 channels. Contractions of endothelium-denuded CA segments to UTP (1-300 μM) and phenylephrine (Phe; 0.1 nM-10 μM) were measured in an isometric tension bath. TRPC1 and TRPC3 mRNA was present in CA of both WKY and SHR. Western blot demonstrated 3.1 ± 1.2 times greater TRPC3 expression and 0.5 ± 0.2 times TRPC1 in SHR versus WKY CA. Isolated CA showed potentiated contraction to UTP in the SHR versus WKY. Activation of voltage-dependent Ca(2+) channels (VDCC) in UTP-mediated constriction only occurred in SHR CA. Contraction to Phe was unaltered between WKY and SHR CA and involved equal significant VDCC activation in both groups. Patch clamp demonstrated that the UTP-stimulated current (I(utp)) was greater in SHR compared to the normotensive WKY and LE rats with peak I(utp) (at -110 mV) of -63 ± 24 pA compared to -25 ± 4 pA, respectively. We demonstrate that UTP-mediated but not Phe-mediated constrictions are potentiated in the CA during hypertension. Expression of TRPC1 is decreased whereas TRPC3 is increased in SHR CA. Interestingly, VDCC activation only contributes to UTP-mediated contraction of SHR CAs whereas it contributes substantially and equally in Phe-mediated contraction. We speculate that the alteration of TRPC channel expression in hypertension leads to greater smooth muscle depolarization, VDCC activation, and vascular contractility in the UTP (but not Phe) signaling pathway.

Functional adaptation of venous smooth muscle response to vasoconstriction in proximal, distal, and varix segments of varicose veins

BACKGROUND

Varicose veins (VarVs) are a common disorder of venous dilation and tortuosity with unclear mechanism. The functional integrity and the ability of various regions of the VarVs to constrict is unclear. This study tested the hypothesis that the different degrees of venodilation in different VarV regions reflect segmental differences in the responsiveness to receptor-dependent vasoconstrictive stimuli and/or in the postreceptor signaling mechanisms of vasoconstriction.

METHODS

Varix segments and adjacent proximal and distal segments were obtained from patients undergoing VarV stripping. Control great saphenous vein specimens were obtained from patients undergoing lower extremity arterial bypass and coronary artery bypass grafting. Circular vein segments were equilibrated under 2 g of tension in a tissue bath, and changes in isometric constriction in response to angiotensin II (AngII, 10(-11)-10(-7) M), phenylephrine (PHE, 10(-9)-10(-4) M), and KCl (96 mM) were recorded. The amount of angiotensin type 1 receptor (AT(1)R) was measured in vein tissue homogenate.

RESULTS

AngII caused concentration-dependent constriction in control vein (max 35.3 +/- 9.6 mg/mg tissue, pED(50) 8.48 +/- 0.34). AngII caused less contraction and was less potent in proximal (max 7.9 +/- 2.5, pED(50) 6.85 +/- 0.61), distal (max 5.7 +/- 1.2, pED(50) 6.74 +/- 0.68), and varix segments of VarV (max 7.2 +/- 2.0, pED(50) 7.11 +/- 0.50), suggesting reduced AT(1)R-mediated contractile mechanisms. VarVs and control veins had similar amounts of AT(1)R. alpha-adrenergic receptor stimulation with PHE caused concentration-dependent constriction in control veins (max 73.0 +/- 13.9 mg/mg tissue, pED(50) 5.48 +/- 0.12) exceeding that of AngII. PHE produced similar constriction and was equally potent in varix and distal segments but produced less constriction and was less potent in proximal segments of VarVs (max 32.1 +/- 6.4 mg/mg tissue, pED(50) 4.89 +/- 0.13) vs control veins. Membrane depolarization by 96 mM KCl, a receptor-independent Ca(2+)-dependent response, produced significant constriction in control veins and similar contractile response in proximal, distal, and varix VarV segments, indicating tissue viability and intact Ca(2+)-dependent contraction mechanisms.

CONCLUSIONS

Compared with control veins, different regions of VarV display reduced AngII-mediated venoconstriction, which may be involved in the progressive dilation in VarVs. Postreceptor Ca(2+)-dependent contraction mechanisms remain functional in VarVs. The maintained alpha-adrenergic responses in distal and varix segments, and the reduced constriction in the upstream proximal segments, may represent a compensatory adaptation of human venous smooth muscle to facilitate venous return from the dilated varix segments of VarV.

Vasodilator effect of ghrelin in the rat aorta

BACKGROUND AND OBJECTIVE

Ghrelin is a hormone mainly produced by the stomach and has been identified as the natural ligand of the growth hormone secretagogue receptor (GHS-R). In addition to its orexigenic effect, ghrelin modulates homeostasis of the cardiovascular system. The aim of this study was to analyze the effect of ghrelin on the vascular reactivity of the aorta.

MATERIAL AND METHODS

This study was performed in the thoracic aorta of 10-12- week-old male Wistar rats. Passive wall tension and contractile responses to angiotensin II (Ang II) (10(-7) mol/l) in the presence of ghrelin (10(-8) mol/l) were evaluated using the organ bath system. The presence of the functional ghrelin receptor, GHS-R 1a, in vascular smooth muscle cells (VSMCs) of the aorta was determined by Western blot.

RESULTS

VSMCs of the vascular wall of the aorta expressed the GHS-R 1a protein. Incubation of the intact aorta with ghrelin (10(-8) mol/l) induced a reduction (p<0.01) in passive wall tension. In endotheliumdenuded aorta, ghrelin did not modify basal vasomotor tone. However, incubation of endothelium-denuded aorta with ghrelin inhibited (p<0.01) Ang II (10(-7) mol/l)-induced vasoconstriction.

CONCLUSIONS

Ghrelin exerts an endothelium-dependent and -independent depressor action on aortic vascular reactivity. These findings provide additional information on the physiological effect of ghrelin on arterial pressure regulation.

The effect of angiotensin II on intracellular pH is mediated by AT1receptor translocation

The effect of ANG II on intracellular pH (pHi) recovery rate and AT1receptor translocation was investigated in transfected MDCK cells. The pHirecovery rate was evaluated by fluorescence microscopy using the fluorescent probe BCECF-AM. The human angiotensin II receptor isoform 1 (hAT1) translocation was analyzed by immunofluorescence and confocal microscope. Our data show that transfected cells in control situation have a pHirecovery rate of 0.219 ± 0.017 pH U/min ( n = 11). This value was similar to nontransfected cells [0.211 ± 0.009 pH U/min ( n = 12)]. Both values were significantly increased with ANG II (10−9M) but not with ANG II (10−6M). Losartan (10−7M) and dimethyl-BAPTA-AM (10−7M) decreased significantly the stimulatory effect of ANG II (10−9M) and induced an increase in Na+/H+exchanger 1 (NHE-1) activity with ANG II (10−6M). Immunofluorescence studies indicated that in control situation, the hAT1receptor was predominantly expressed in cytosol. However, it was translocated to plasma membrane with ANG II (10−9M) and internalized with ANG II (10−6M). Losartan (10−7M) induced hAT1translocation to plasma membrane in all studied groups. Dimethyl-BAPTA-AM (10−7M) did not change the effect of ANG II (10−9M) on the hAT1receptor distribution but induced its accumulation at plasma membrane in cells treated with ANG II (10−6M). With ionomycin (10−6M), the receptor was accumulated in cytosol. The results indicate that, in MDCK cells, the effect of ANG II on NHE-1 activity is associated with ligand binding to AT1receptor and intracellular signaling events related to AT1translocation.

Increased store-operated and 1-oleoyl-2-acetyl-sn-glycerol-induced calcium influx in monocytes is mediated by transient receptor potential canonical channels in human essential hypertension

OBJECTIVE

Activation of nonselective cation channels of the transient receptor potential canonical (TRPC) family has been associated with hypertension. Whether store-operated channels, which are activated after depletion of intracellular stores, or second-messenger-operated channels, which are activated by 1-oleoyl-2-acetyl-sn-glycerol, are affected in essential hypertension is presently unknown.

METHODS

Using a polymerase chain reaction, an in-cell western assay and the fluorescent dye technique we studied TRPC3, TRPC5, and TRPC6 expression and store-operated and 1-oleoyl-2-acetyl-sn-glycerol-induced calcium influx into human monocytes in 19 patients with essential hypertension and in 17 age-matched and sex-matched normotensive control individuals.

RESULTS

We observed a significantly increased expression of TRPC3 and TRPC5, but not TRPC6, in essential hypertension. Store-operated calcium influx was significantly elevated in essential hypertension. Store-operated calcium influx was reduced by the inhibitor 2-aminoethoxydiphenylborane, specific TRPC3 and TRPC5 knockdown, but not TRPC6 knockdown using gene silencing by RNA interference. 1-Oleoyl-2-acetyl-sn-glycerol-induced calcium influx and barium influx were also significantly elevated in essential hypertension. The 1-oleoyl-2-acetyl-sn-glycerol-induced cation influx was reduced by TRPC3 and TRPC5 knockdown.

CONCLUSION

We demonstrated an increased TRPC3 and TRPC5 expression and a subsequently increased store-operated calcium influx and increased 1-oleoyl-2-acetyl-sn-glycerol-induced cation influx in monocytes of patients with essential hypertension. This increased activation of monocytes through TRPC channels in patients with essential hypertension may promote vascular disease in these patients.

Transient receptor potential channels in essential hypertension

OBJECTIVE

The role of nonselective cation channels of the transient receptor potential channel (TRPC) family in essential hypertension has not yet been investigated.

METHODS

We studied TRPCs in 51 patients with essential hypertension and 51 age-matched and sex-matched normotensive control subjects. Calcium and gadolinium influx into human monocytes was determined using the fluorescent dye technique. TRPC expression was measured using reverse transcriptase-polymerase chain reaction and in-cell western assay. Gene silencing by small interfering RNA for specific TRPC knockdown was also performed.

RESULTS

We observed an increased gadolinium/calcium-influx ratio through TRPC in essential hypertensive patients compared with normotensive control subjects [cation influx ratio (mean +/- SEM), 125 +/- 14 versus 80 +/- 7%; each n = 51; P < 0.01], due to an increase of gadolinium influx in hypertensive patients compared with normotensive control subjects (48 +/- 4 versus 36 +/- 3%; each n = 51; P < 0.05). We observed a significant increase of TRPC3 and TRPC5 protein expression in essential hypertensive patients compared with normotensive control subjects (normalized TRPC3 expression, 3.21 +/- 0.59 versus 1.36 +/- 0.07; each n = 20; P < 0.01; normalized TRPC5 expression, 2.10 +/- 0.28 versus 1.40 +/- 0.52; each n = 12; P < 0.05). We used small interfering RNA for knockdown of TRPC5. The thereby reduced channel expression caused a significant attenuation of calcium and gadolinium influx.

CONCLUSION

This study points to an important role of TRPCs in essential hypertension.

The inhibitory effect of leptin on angiotensin II-induced vasoconstriction is blunted in spontaneously hypertensive rats

OBJECTIVE

Leptin attenuates the angiotensin II-induced increase of cytosolic calcium ([Ca2+]i) and vasoconstriction in the aorta of normotensive Wistar rats. To determine whether these effects may be altered in hypertension, we assessed the effect of leptin on angiotensin II-induced vascular response in the aorta of 10-week-old spontaneously hypertensive rats (SHR).

METHODS

Contractile responses to angiotensin II (100 nmol/l) in the presence of different concentrations of leptin (0.1, 1, 10, 100 nmol/l) were evaluated in isolated aortic rings by the organ bath system. [Ca2+]i was measured in vascular smooth muscle cells (VSMCs) using Fura-2 fluorescence. The expression of the short (OB-Ra) and long (OB-Rb) isoforms of the leptin receptor in VSMCs was evaluated by real-time reverse transcriptase-polymerase chain reaction and western-blot analysis.

RESULTS

Circulating leptin concentrations were increased in SHR. Serum metabolic parameters, including glucose, insulin, total cholesterol and triglyceride levels, were also elevated in SHR. Leptin did not modify the angiotensin II-induced vasoconstriction in SHR either in intact or endothelium-denuded aortic rings. In addition, leptin was not able either to diminish the angiotensin II-induced the peak rise of [Ca2+]i or to accelerate the recovery rate to basal calcium levels in VSMCs from SHR. However, OB-Ra and OB-Rb mRNA and protein expression were increased in SHR VSMCs.

CONCLUSIONS

The lack of effect of leptin on angiotensin II-induced contraction in the aorta of SHR is due to an impaired handling of [Ca2+]i in VSMCs. Hyperleptinemia and overexpression of OB-R in VSMCs could be compensatory mechanisms against VSMC leptin resistance in genetically hypertensive rats.

Role of L-type calcium channel blocking in epidermal growth factor receptor-independent activation of extracellular signal regulated kinase 1/2

OBJECTIVE

Vascular smooth muscle cell (VSMC) differentiation, growth and survival, key events in the development of cardiovascular diseases, are under the control of signaling enzymes including extracellular signal regulated kinase 1/2 (ERK 1/2), Akt and epidermal growth factor receptor (EGFR) activation. EGFR trans-activation is known to mediate thrombin- or angiotensin II (AII)-stimulated ERK 1/2 activation. However, our laboratory has demonstrated, in thrombin-stimulated VSMC, that the prevention of intracellular Ca2+ elevation ([Ca2+]i) by BAPTA-AM pretreatment unveiled EGFR-independent ERK 1/2 activation. Since calcium channel blockers (CCBs) also impair agonist-induced [Ca2+]i elevation, we investigated whether EGFR-independent ERK 1/2 activation could occur in VSMCs treated by CCBs such as amlodipine, isradipine and verapamil, and examined the possible role of Akt.

METHODS

Cultured VSMCs were pretreated or not with CCBs and with various inhibitors of the signaling pathways under study, prior to stimulation by thrombin or AII, and the phosphorylation/activation status of EGFR, Akt and ERK 1/2 was determined by Western blotting using phospho-specific antibodies.

RESULTS AND CONCLUSION

Unlike BAPTA, CCBs did not impair stimulus-induced EGFR trans-activation, hence ERK1/2 phosphorylation. However, when EGFR kinase was inhibited, CCBs and BAPTA dose-dependently protected stimulus-induced ERK1/2 phosphorylation. The effect of amlodipine could not be mimicked by its R+ enantiomer, which is devoid of CCB activity, suggesting that the effects of CCBs were accounted for by their L-type Ca2+ channel-blocking property. Altogether, our results indicated that in G-protein-coupled receptor (GPCR)-stimulated VSMCs, the prevention of [Ca2+]i elevation by CCBs unmasked an EGFR kinase-independent phosphorylation of ERK 1/2. Since EGFR kinase inhibitors are supposed to be efficient in the treatment of some cancers, such a mechanism might be clinically relevant in hypertensive patients with cancer.

Contractile Responses of Aortae from WKY and SHR to Vasoconstrictors

Aortae taken from spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats aged 4, 8 and 16 weeks were prepared as rings and used to measure the effects of five vasoconstrictors. The endothelium was removed in order to measure selectively the contractile responses induced by potassium chloride (KCl), phenylephrine (PHE), angiotensin-II (Ang II), endothelin-1 (ET-1) and human urotensin-II (U-II). These responses were assumed to derive from the activation of specific receptors (namely alpha1, AT1, ETA and UT-II) or from depolarization of the smooth muscle fibers by KCl. Specific antagonists prazosin, losartan, BQ-123 and [Orn8]-UII were used at various concentrations for a pharmacological characterization of these latter receptor systems. The primary purpose of the study was to explore mechanisms or factors that may intervene in the development and maintenance of high blood pressure in SHR. Results indicate that isolated aortae of SHR and WKY contain contractile sites (receptors) whose pharmacological profiles (pEC50 for agonists, pA2 for antagonists) are very similar to those of other biological systems and should be considered as typical for the alpha1, AT1, ETA and UT-II receptor types. Aortae taken from SHR 4 (non hypertensive), 8 and 16 weeks old (hypertensive) responded to the vasoconstrictors with reduced maximal contractions compared to those of age-matched WKY. These unexpected reduced responses of aortae, observed with the five vasoconstrictors, may be attributed to a non specific lesions. Maximal contraction of aortae from SHR increased from 4 to 16 weeks for KCI, PHE and U-II, decreased for Ang II, and remained stable for ET-1. There was also an age-dependent increase of maximal contraction induced by U-II in WKY. It is suggested that aortae from SHR undergo early remodelling that leads to reduced contractility in vitro and possibly to vessel rigidity in vivo. The factors involved in this process appear to be of genetic origin since they are present before hypertension: they may contribute to modify aortic compliance and perhaps vascular resistance in hypertensive animals and thus being the cause and not the consequence of high blood pressure.

Oxidative and calcium stress regulate DSCR1 (Adapt78/MCIP1) protein

DSCR1 (adapt78) is a stress-inducible gene and cytoprotectant. Its protein product, DSCR1 (Adapt78), also referred to as MCIP1, inhibits intracellular calcineurin, a phosphatase that mediates many cellular responses to calcium. Exposure of human U251 and HeLa cells to hydrogen peroxide led to a rapid hyperphosphorylation of DSCR1 (Adapt78). Inhibitor and agonist studies revealed that a broad range of kinases were not responsible for DSCR1 (Adapt78) hyperphosphorylation, including ERK1/2, although parallel activation of the latter was observed. Phosphorylation of both DSCR1 (Adapt78) and ERK1/2 was attenuated by inhibitors of tyrosine phosphatase, suggesting the common upstream involvement of tyrosine dephosphorylation. The hyperphosphorylation electrophoretic shift in DSCR1 (Adapt78) mobility was also observed with other oxidizing agents (peroxynitrite and menadione) but not nonoxidants. Calcium ionophores strongly induced the levels of both hypo- and hyper-phosphorylated DSCR1 (Adapt78) but did not alter phosphorylation status. Calcium-dependent growth factor- and angiotensin II-stimulation also induced both DSCR1 (Adapt78) species. Phosphorylation of either or both serines in a 13-amino acid peptide made to a calcineurin-interacting conserved region of DSCR1 (Adapt78) attenuated inhibition of calcineurin. These data indicate that DSCR1 (Adapt78) protein is a novel, early stage oxidative stress-activated phosphorylation target and newly identified calcium-inducible protein, and suggest that these response mechanisms may contribute to the known cytoprotective and calcineurin-inhibitory activities of DSCR1 (Adapt78).

Recent advances in angiotensin II signaling

Angiotensin II (Ang II) is a multifunctional hormone that influences the function of cardiovascular cells through a complex series of intracellular signaling events initiated by the interaction of Ang II with AT1 and AT2 receptors. AT1 receptor activation leads to cell growth, vascular contraction, inflammatory responses and salt and water retention, whereas AT2 receptors induce apoptosis, vasodilation and natriuresis. These effects are mediated via complex, interacting signaling pathways involving stimulation of PLC and Ca2+ mobilization; activation of PLD, PLA2, PKC, MAP kinases and NAD(P)H oxidase, and stimulation of gene transcription. In addition, Ang II activates many intracellular tyrosine kinases that play a role in growth signaling and inflammation, such as Src, Pyk2, p130Cas, FAK and JAK/STAT. These events may be direct or indirect via transactivation of tyrosine kinase receptors, including PDGFR, EGFR and IGFR. Ang II induces a multitude of actions in various tissues, and the signaling events following occupancy and activation of Ang receptors are tightly controlled and extremely complex. Alterations of these highly regulated signaling pathways may be pivotal in structural and functional abnormalities that underlie pathological processes in cardiovascular diseases such as cardiac hypertrophy, hypertension and atherosclerosis.

Comparison of angiotensin II (Ang II) effects in the internal anal sphincter (IAS) and lower esophageal sphincter smooth muscles

Studies were performed to compare the actions of Ang II in the internal anal sphincter (IAS) vs. lower esophageal sphincter (LES) smooth muscles in vitro, in opossum and rabbit. Studies also were carried out in isolated smooth muscle cells. In opossum, Ang II produced no discernible effects in the IAS, but did produce a concentration-dependent contraction in the LES. Conversely, in the rabbit, while Ang II caused a modest response in the LES, it caused a significant contraction in the IAS. The contractile responses of Ang II in the opossum LES were mostly resistant to different neurohumoral antagonists but were antagonized by AT1 antagonist losartan. AT2 antagonist PD 123,319, rather than inhibiting, prolonged the contractile action of Ang II. The contractile actions of Ang II in the opossum LES were not modified by the tyrosine kinase inhibitors (genistein and tyrphostin 1 x 10(-6) M) but were partially attenuated by the PKC inhibitor H-7 (1 x 10(-6) M), Ca2+ channel blocker nicardipine (1 x 10(-5) M), Rho kinase inhibitor HA-1077 (1 x 10(-7) M) or p(44/42) MAP kinase inhibitor PD 98059 (5 x 10(-5) M). The combination of HA-1077 and H-7 did not cause an additive attenuation of Ang II responses. Western blot analyses revealed the presence of both AT1 and AT2 receptors. We conclude that Ang lI-induced contraction of sphincteric smooth muscle occurs primarily by the activation of AT1 receptors at the smooth muscle cells and involves multiple pathways, influx of Ca2+, and PKC, Rho kinase and p(44/42) MAP kinase.

Animal model for angiotensin II effects in the internal anal sphincter smooth muscle: mechanism of action

Effect of ANG II was investigated in in vitro smooth muscle strips and in isolated smooth muscle cells (SMC). Among different species, rat internal and sphincter (IAS) smooth muscle showed significant and reproducible contraction that remained unmodified by different neurohumoral inhibitors. The AT(1) antagonist losartan but not AT(2) antagonist PD-123319 antagonized ANG II-induced contraction of the IAS smooth muscle and SMC. ANG II-induced contraction of rat IAS smooth muscle and SMC was attenuated by tyrosine kinase inhibitors genistein and tyrphostin, protein kinase C (PKC) inhibitor H-7, Ca(2+) channel blocker nicardipine, Rho kinase inhibitor Y-27632 or p(44/42) mitogen-activating protein kinase (MAPK(44/42)) inhibitor PD-98059. Combinations of nicardipine and H-7, Y-27632, and PD-98059 caused further attenuation of the ANG II effects. Western blot analyses revealed the presence of both AT(1) and AT(2) receptors. We conclude that ANG II causes contraction of rat IAS smooth muscle by the activation of AT(1) receptors at the SMC and involves multiple intracellular pathways, influx of Ca(2+), and activation of PKC, Rho kinase, and MAPK(44/42).

Increased Ca2+ buffering function of sarcoplasmic reticulum in small mesenteric arteries from spontaneously hypertensive rats

We compared the Ca2+ buffering function of the superficial sarcoplasmic reticulum (SR) during rest and during contraction in endothelium-denuded strips of small mesenteric arteries from 13-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The addition of caffeine (1-20 mM) caused a transient contraction in both strains, and the contraction was significantly larger in SHR. When the SR Ca2+ buffering function was eliminated by cyclopiazonic acid (CPA; 10 microM) or thapsigargin (100 nM), both of which inhibit SR Ca2+-ATPase, or by ryanodine (10 microM), which depletes the SR Ca2+, there was a larger contraction in SHR than in WKY, suggesting that the Ca2+ buffering function of the SR during rest is more important in SHR than in WKY. Judging from the augmenting effects of these three agents on the contractile responses to Bay k 8644 (1-300 nM), an agonist of L-type Ca2+ channels, or norepinephrine (10(-9)-10(-4) M), an alpha-adrenoceptor agonist, the effects were significantly greater in SHR than in WKY. We conclude that 1) the Ca2+ influx during rest and during stimulation with Bay k 8644 or norepinephrine is strongly buffered by Ca2+ uptake into the superficial SR in the small mesenteric arteries from SHR and WKY; and 2) these Ca2+ buffering functions are increased in SHR because of the larger capacity of SR for Ca2+ storage.

Angiotensin receptors: signaling, vascular pathophysiology, and interactions with ceramide

Angiotensin II (ANG II) is a pleiotropic vasoactive peptide that binds to two distinct receptors: the ANG II type 1 (AT(1)) and type 2 (AT(2)) receptors. Activation of the renin-angiotensin system (RAS) results in vascular hypertrophy, vasoconstriction, salt and water retention, and hypertension. These effects are mediated predominantly by AT(1) receptors. Paradoxically, other ANG II-mediated effects, including cell death, vasodilation, and natriuresis, are mediated by AT(2) receptor activation. Our understanding of ANG II signaling mechanisms remains incomplete. AT(1) receptor activation triggers a variety of intracellular systems, including tyrosine kinase-induced protein phosphorylation, production of arachidonic acid metabolites, alteration of reactive oxidant species activities, and fluxes in intracellular Ca(2+) concentrations. AT(2) receptor activation leads to stimulation of bradykinin, nitric oxide production, and prostaglandin metabolism, which are, in large part, opposite to the effects of the AT(1) receptor. The signaling pathways of ANG II receptor activation are a focus of intense investigative effort. We critically appraise the literature on the signaling mechanisms whereby AT(1) and AT(2) receptors elicit their respective actions. We also consider the recently reported interaction between ANG II and ceramide, a lipid second messenger that mediates cytokine receptor activation. Finally, we discuss the potential physiological cross talk that may be operative between the angiotensin receptor subtypes in relation to health and cardiovascular disease. This may be clinically relevant, inasmuch as inhibitors of the RAS are increasingly used in treatment of hypertension and coronary heart disease, where activation of the RAS is recognized.

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.

Norepinephrine-induced calcium signaling pathways in afferent arterioles of genetically hypertensive rats

This study provides new information about the relative importance of calcium mobilization and entry in the renal vascular response to adrenoceptor activation in afferent arterioles isolated from 7- to 8-wk-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Intracellular free calcium concentration ([Ca(2+)](i)) was measured in microdissected arterioles utilizing ratiometric photometry of fura 2 fluorescence. There was no significant strain difference in baseline [Ca(2+)](i). Norepinephrine (NE; 10(-6) and 10(-7) M) elicited immediate, sustained increases in [Ca(2+)](i). The general temporal pattern of response to 10(-6) M NE consisted of an initial peak and a maintained plateau phase. The response to NE was partially blocked by nifedipine (10(-6) M) or 8-(N,N-diethylamino) octyl-3,4,5-trimetoxybenzoate (TMB-8; 10(-5) M). A calcium-free external solution abolished the sustained [Ca(2+)](i) plateau response to NE, with less influence on the peak response. In the absence of calcium entry, TMB-8 (10(-5) M) completely blocked the calcium response to NE in WKY but not SHR, suggesting strain differences in mobilization. A higher concentration of TMB-8 (10(-4) M), however, blocked all discernible mobilization in both strains. We conclude that there are differences in Ca(2+) handling in renal resistance vessels between young WKY and SHR with respect to mobilization stimulated by alpha-adrenoceptors. Afferent arterioles of young SHR appear to have a larger inositol-1,4,5-trisphosphate-sensitive pool or release from a site less accessible to TMB-8.

Effect of insulin and angiotensin II on cell calcium in human skin fibroblasts

We have recently shown that insulin attenuates angiotensin II-induced intracellular Ca(2+) mobilization in human skin fibroblasts from normotensive subjects. This study was designed to investigate the effects of angiotensin II and the interactions between insulin and angiotensin II on intracellular Ca(2+) mobilization in skin fibroblasts from patients with essential hypertension. Fibroblasts were obtained from 9 normotensives and 18 hypertensives. Spectrofluorophotometric free Ca(2+) measurement was performed in monolayers of 24-hour serum-deprived cells. Resting intracellular Ca(2+) level and angiotensin II-stimulated intracellular Ca(2+) peak were higher in fibroblasts from hypertensives compared with those from normotensives. The effect of acute insulin exposure was evaluated in fibroblasts from hypertensives subdivided on the basis of insulin sensitivity. In insulin-sensitive hypertensives, insulin significantly blunted the effects of angiotensin II on intracellular Ca(2+) response, whereas in insulin-resistant patients, insulin did not modify intracellular Ca(2+) response to angiotensin II. Pertussis toxin, a G(ialpha)-inhibitor, reduced angiotensin II-stimulated Ca(2+) peak in insulin-sensitive but not in insulin-resistant hypertensives. In conclusion, the effects of angiotensin II on intracellular Ca(2+) mobilization are more pronounced in fibroblasts from hypertensives compared with those from normotensives, and the inhibitory effect of insulin is blunted in insulin-resistant hypertensives by a G(ialpha) pertussis toxin-sensitive abnormality.

Effect of extracellular matrix elements on angiotensin II-induced calcium release in vascular smooth muscle cells from normotensive and hypertensive rats

The interaction of the vascular smooth muscle cells (VSMCs) with the components of the matrix determines several functions of the cell, such as growth and differentiation. In contrast, an alteration in angiotensin (Ang) II-induced Ca(2+) mechanisms in VSMCs was reported in genetic hypertension. In this study, we wished to assess the effect of different components of the extracellular matrix on the increase of [Ca(2+)](i) induced by Ang II in VSMCs from spontaneously hypertensive rats (SHR) compared with those from normotensive Wistar-Kyoto rats (WKY). Results demonstrate for the first time that elements of the extracellular matrix modulate the Ang II-induced Ca(2+) transport mechanisms. This modulation is different in cells from WKY compared with those from SHR. Thus, growing cells from SHR on collagen I, collagen IV, fibronectin, vitronectin, or Matrigel induced a significant decrease in Ang II-induced Ca(2+) release from internal stores, whereas in cells from WKY, no effect could be observed except for those grown on collagen I, which increased Ca(2+) release. Fibronectin and vitronectin, however, induced a decrease in Ang II-induced Ca(2+) influx in WKY, whereas no effect could be observed in SHR. Conversely, collagen I and collagen IV induced an increase in this influx in SHR but not in WKY, whereas Matrigel increased the influx in both strains. These results suggest a modulation of the Ang II-associated signaling events by the matrix elements via the focal adhesion points. The understanding of these synergies should provide insight into issues such as development of hypertrophy of large vessels in hypertension.

Lead–cadmium interaction effect on the responsiveness of rat mesenteric vessels to norepinephrine and angiotensin II

The comparison of the reactivity to norepinephrine (NE) and angiotensin II (A II) of isolated mesenteric blood vessels obtained from rats simultaneously poisoned with lead and cadmium to those responses of rats treated singly with lead or cadmium was performed. Male Buffalo rats aged 6-8 weeks were administered intragastrically with lead (35 mg Pb/kg body wt.) and/or cadmium (5 mg Cd/body wt.), once a week for a period of 7 weeks. Control rats were given equimolar amounts of sodium acetate and/or sodium chloride. Changes in mesenteric vascular resistance due to NE and A II injections were measured ex vivo as an increase in perfusion pressure in vessels prepared by McGregor's method. The dose-response curve for NE (0.01-5.0 microg) determined for vessels of rats poisoned simultaneously with lead and cadmium was shifted to the left in comparison to controls (not poisoned rats), similarly to these determined for rats poisoned with lead or cadmium. ED(50) NE pointed out in the control group (0.83+/-0.5 microg) was significantly greater than in metal treated groups (0.44+/-0.09; 0.45+/-0.26 and 0.5+/-0.11 microg in lead, cadmium, lead and cadmium-treated rats, respectively). This study indicated a tachyphylaxis in responses of isolated mesenteric vessels to A II injected in increasing doses, and the weaker, in comparison to controls, response of vessels of rats poisoned with lead and/or cadmium to A II at a dose of 0.4 microg. The decreasing response to A II could result from changes in calcium ions transport through L-type channels in vascular smooth muscle cells, because verapamil (2.0 microM) inhibited the A II-induced vasoconstriction more weakly in rats poisoned with metals than in controls. Inhibitor of prostaglandins synthesis, ketoprofen (200 microg/ml per min.) attenuated the pressor effect of NE in blood vessels obtained from all rats, but this effect was less potent in arteries of cadmium poisoned rats. Ketoprofen also inhibited the vasoconstrictory action of A II in all groups, but this effect was lower in vessels of rats poisoned simultaneously with lead and cadmium. We suggest that the release of vasoactive prostaglandins as a consequence of endothelial angiotensin receptor stimulation changes more under the influence of metals administered to rats simultaneously than under the influence or lead or cadmium administered singly. Treatment with a nitric oxide synthase inhibitor (L-NOARG; 22 microg/ml per min.) potentiated a NE-induced pressor response in all groups. However, the increase in perfusion pressure was greater in rats poisoned with cadmium in comparison to controls. L-NOARG potentiated the A II induced vasoconstriction only in cadmium poisoned rats, also indicating a greater influence of nitric oxide in cadmium treated rat vasculature. Two-way ANOVA showed the existence of lead-cadmium interactions effects on the reactivity of rat isolated mesenteric vessels to NE, A II and papaverine.

Role of c-Src in the regulation of vascular contraction and Ca2+ signaling by angiotensin II in human vascular smooth muscle cells

OBJECTIVE

Tyrosine kinases, typically associated with growth-signaling pathways, also play a role in Ang II-stimulated vascular contraction. However the specific kinases involved are unclear. We hypothesize here that c-Src, a non-receptor tyrosine kinase, is an important upstream regulator of vascular smooth muscle cell (VSMC) Ca2+ signaling and associated vascular contraction induced by Ang II.

METHODS

Cultured VSMCs from resistance arteries of healthy subjects were studied. Human VSMCs electroporated with anti-c-Src antibody and c-Src-deficient VSMCs from small arteries of c-Src knockout mice (Src-/-mVSMCs) were also investigated. Intracellular free Ca2+ concentration ([Ca2+]i), c-Src activity and IP3 production were measured by fura 2, immunoblot and radioimmunoassay respectively. Contraction was examined in intact rat small arteries.

RESULTS

Ang II rapidly increased VSMC c-Src activity, with peak responses obtained at 1 min. Ang II induced a biphasic [Ca2+]i response (Emax = 636 +/- 123 nmol/l). The initial [Ca2+]i transient, mediated primarily by Ca2+mobilization, was dose-dependently attenuated by the selective Src inhibitor, PP2, but not by PP3 (inactive analogue). Ang II-elicited [Ca2+]i responses were blunted in cells electroporated with anti-c-Src antibodies and in c-Src-/-mVSMCs. Src inhibition decreased Ang II-induced generation of IP3 in human VSMCs. Ang II dose-dependently increased vascular contraction (Emax = 40 +/- 6.5%). These responses were attenuated by PP2 (Emax = 7.8 +/- 0.08%) but not by PP3 (Emax = 35 +/- 4.5%).

CONCLUSIONS

Our findings identify c-Src as an important regulator of VSMC [Ca2+]i signaling and implicate a novel contractile role for this non-receptor tyrosine kinase in Ang II-stimulated vascular smooth muscle.

Structure and mechanical properties of resistance arteries in hypertension: role of adhesion molecules and extracellular matrix determinants

Abnormalities of resistance arteries may play a role in the pathogenesis and pathophysiology of hypertension in experimental animals and humans. Vessels that, when relaxed, measure <400 microm in lumen diameter act as the major site of vascular resistance and include a network of small arteries (lumen approximately 100 to 400 microm) and arterioles (<100 microm). Because increased peripheral resistance is generated by a narrowed lumen diameter, significant effort has been focused on determining the mechanisms that reduce lumen size. Three important vascular components are clearly involved, including alterations of vascular structure, mechanics (stiffness), and function. Structural abnormalities comprise a reduced lumen diameter and thickening of the vascular media, resulting in an increased media-lumen ratio. Changes in the mechanical properties of an artery, particularly increased stiffness, may also result in a reduced lumen diameter. These vascular abnormalities may be caused or influenced by the expression and/or topographic localization of extracellular matrix components, such as collagen and elastin, and by changes in cell-extracellular fibrillar attachment sites, such as adhesion molecules like integrins. This article discusses the abnormalities of resistance arteries in hypertension and reviews the evidence suggesting an important role for adhesive and extracellular matrix determinants.

Effect of oral magnesium supplementation on blood pressure, platelet aggregation and calcium handling in deoxycorticosterone acetate induced hypertension in rats

OBJECTIVE

To study the effect of oral magnesium supplementation on blood pressure, platelet aggregation and platelet calcium handling in deoxycorticosterone acetate (DOCA)-induced hypertension in rats.

DESIGN AND METHODS

Rats were divided into four groups of 20 each. Drug treatments were given for a 6-week period. Control rats were vehicle treated. In the second group, DOCA, 15 mg/kg, was injected subcutaneously twice weekly with 1% NaCl used instead of drinking water. The third group was given magnesium oxide (MgO), 1 g/kg daily, orally by gavage. The fourth group was given MgO along with DOCA and 1% NaCl. Blood pressure and heart rate were measured weekly. Platelet aggregation, intracellular calcium, calcium uptake and calcium efflux studies were performed at the end of sixth week. Serum magnesium concentration, plasma levels of reactive nitrogen intermediates (RNI) and citrulline were also measured

RESULTS

There was a significant rise in blood pressure in the DOCA-treated rats. Magnesium prevented the gradual rise in blood pressure when given along with DOCA, but had no effect in normotensive rats. Heart rate did not show any significant change. Platelet aggregation was significantly reduced in all the treatment groups compared to the control group. DOCA treatment produced a significant increase in the intracellular calcium concentration as well as the calcium uptake compared to the control group. Magnesium supplementation inhibited the increased intracellular calcium concentration and calcium uptake in DOCA-treated rats. RNI and citrulline levels were elevated in all the treatment groups. Serum magnesium levels were significantly higher in the magnesium-treated and DOCA plus magnesium-treated rats.

CONCLUSIONS

Magnesium supplementation prevents blood pressure elevation in DOCA hypertensive rats. These effects are associated with inhibition of platelet calcium uptake and decreased intracellular free calcium concentration.

Transforming growth factor-beta1 modulates angiotensin II-induced calcium release in vascular smooth muscle cells from spontaneously hypertensive rats

OBJECTIVES

To investigate the role of transforming growth factor-beta1 (TGF-beta1) on Ca2+-dependent mechanisms elicited by angiotensin II in aortic vascular smooth muscle cells (VSMC) of Wistar- Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

METHODS

Cai2+ release induced by angiotensin II (1 micromol/ l) was studied in cultured VSMC isolated from the aortas of 6-week-old WKY rats and SHR. Intracellular Ca2+ (Cai2+) was assessed in Fura-2 loaded cells using fluorescent imaging microscopy. Angiotensin II receptors were analysed by binding studies.

RESULTS

Pretreatment of VSMC for 24 h with TGF-beta1 significantly increased angiotensin II-induced Cai2+ mobilization from internal stores in SHR, while Ca2+ influx was not altered. This effect involves tyrosine kinase and is not due to an increase in angiotensin II binding sites, or a change in the affinity of the receptors. By contrast, TGF-beta1 did not modify the response of VSMC from WKY rats to angiotensin II.

CONCLUSIONS

These results help our understanding of the interactions between the pathways activated by TGF-beta1 and the G protein-coupled receptor signalling pathway, and their role in genetic hypertension.

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

This study examined whether alterations in intracellular or extracellular Ca2+ mobilization were related to differences in caffeine and phenylephrine (PHE)-induced contractions between two-kidney. one-clip hypertensive (2K-1C) and normotensive (2K) rat aortas. After depletion and reloading of intracellular Ca2+ stores, caffeine and PHE-induced contractions in Ca2+-free solution were increased in 2K-1C. Thapsigargin reduced the contraction to caffeine in 2K-1C and 2K with similar sensitivity. PHE-induced contraction in 1.6-mM Ca2+ solution was decreased in 2K-1C, and nifedipine was less effective in lowering this response. The responsiveness to extracellular Ca2+ was decreased in 2K-1C hypertensive rat aortas. Our results indicate an increased intracellular Ca2+ stores that are not related to alteration in Ca2+-ATPase function and a lower contribution of L-type channels to the contraction of 2K-1C aortas.

Activation of the Na(+)-H+ exchanger modulates angiotensin II-stimulated Na(+)-dependent Mg2+ transport in vascular smooth muscle cells in genetic hypertension

This study investigated the role of the Na(+)-H+ exchanger (NHE) on angiotensin II (Ang II)-induced activation of Na(+)-dependent Mg2+ transport in vascular smooth muscle cells (VSMCs) from Wistar-Kyoto rats (WKY; n=20) and spontaneously hypertensive rats (SHR; n=20). Intracellular free concentrations of Mg2+ ([Mg2+]i) and Na+ ([Na+]i) and intracellular pH (pHi) were measured with the specific fluorescent probes mag-fura 2-AM, SBFI-AM, and BCECF-AM, respectively. Na+ dependency of Mg2+ transport was assessed in Na(+)-free buffer, and the role of the NHE was determined with the highly selective NHE blocker 5-(N-methyl-N-isobutyl) amiloride (MIA). Basal [Mg2+]i was lower in SHR than WKY (0.59+/-0.01 versus 0.71+/-0.01 mmol/L, P<0.05). Basal pHi and [Na+]i were not different between the 2 groups. Ang II dose dependently increased [Na+]i and pHi and decreased [Mg2+]i. Responses were significantly greater (P<0.05) in SHR versus WKY ([Na+]i E(max)=37.5+/-1.1 versus 33.7+/-1.9 mmol/L; pHi E(max)=7.35+/-0.04 versus 7.20+/-0.01; [Mg2+]i E(min)=0. 28+/-0.09 versus 0.53+/-0.02 mmol/L, SHR versus WKY). In Na(+)-free buffer, Ang II-elicited [Mg2+]i responses were inhibited. MIA (1 micromol/L) inhibited Ang II-stimulated responses in WKY and normalized responses in SHR ([Mg2+]i E(min)=0.49+/-0.02). Ang II-stimulated activation of NHE was significantly increased (P<0.05) in SHR (0.07+/-0.002 DeltapH(i)/s) compared with WKY (0.05+/-0.004 DeltapH(i)/s). These data demonstrate that in VSMCs [Mg2+]i regulation is Na+ dependent, that activation of NHE modulates Na(+)-Mg2+ transport, and that increased activity of NHE may play a role in altered Na(+)-dependent regulation of [Mg2+]i in SHR.

Mitogen-activated protein/extracellular signal-regulated kinase inhibition attenuates angiotensin II-mediated signaling and contraction in spontaneously hypertensive rat vascular smooth muscle cells

This study investigates the role of extracellular signal-regulated kinases (ERKs) in angiotensin II (Ang II)-generated intracellular second messengers (cytosolic free Ca2+ concentration, ie, [Ca2+]i, and pHi) and in contraction in isolated vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY) using the selective mitogen-activated protein (MAP)/ERK inhibitor, PD98059. VSMCs from mesenteric arteries were cultured on Matrigel basement membrane matrix. These cells, which exhibit a contractile phenotype, were used to measure [Ca2+]i, pHi, and contractile responses to Ang II (10(-12) to 10(-6) mol/L) in the absence and presence of PD98059 (10(-5) mol/L). [Ca2+]i and pHi were measured by fura-2 and BCECF methodology, respectively, and contraction was determined by photomicroscopy. Ang II-stimulated ERK activity was measured by Western blot analysis using a phospho-specific ERK-1/ERK-2 antibody and by an MAPK enzyme assay. Ang II increased [Ca2+]i and pHi and contracted cells in a dose-dependent manner. Maximum Ang II-elicited contraction was greater (P<0.05) in SHR (41.9+/-5.1% reduction in cell length relative to basal length) than in WKY (28.1+/-3.0% reduction in cell length relative to basal length). Basal [Ca2+]i, but not basal pHi, was higher in SHR compared with WKY. [Ca2+]i and pHi effects of Ang II were enhanced (P<0.05) in SHR compared with WKY (maximum Ang II-induced response [Emax] of [Ca2+]i, 576+/-24 versus 413+/-43 nmol/L; Emax of pHi, 7.33+/-0.01 versus 7.27+/-0.03, SHR versus WKY). PD98059 decreased the magnitude of contraction and attenuated the augmented Ang II-elicited contractile responses in SHR (Emax,19. 3+/-3% reduction in cell length relative to basal length). Ang II-stimulated [Ca2+]i (Emax, 294+/-55 nmol/L) and pHi (Emax, 7. 27+/-0.04) effects were significantly reduced by PD98059 in SHR. Ang II-induced ERK activity was significantly greater (P<0.05) in SHR than in WKY. In conclusion, Ang II-stimulated signal transduction and associated VSMC contraction are enhanced in SHR. MAP/ERK inhibition abrogated sustained contraction and normalized Ang II effects in SHR. These data suggest that ERK-dependent signaling pathways influence contraction and that they play a role in vascular hyperresponsiveness in SHR.