New Insights in the Contribution of Voltage-Gated Nav Channels to Rat Aorta Contraction

BACKGROUND: Despite increasing evidence for the presence of voltage-gated Na(+) channels (Na(v)) isoforms and measurements of Na(v) channel currents with the patch-clamp technique in arterial myocytes, no information is available to date as to whether or not Na(v) channels play a functional role in arteries. The aim of the present work was to look for a physiological role of Na(v) channels in the control of rat aortic contraction. METHODOLOGY/PRINCIPAL FINDINGS: Na(v) channels were detected in the aortic media by Western blot analysis and double immunofluorescence labeling for Na(v) channels and smooth muscle alpha-actin using specific antibodies. In parallel, using real time RT-PCR, we identified three Na(v) transcripts: Na(v)1.2, Na(v)1.3, and Na(v)1.5. Only the Na(v)1.2 isoform was found in the intact media and in freshly isolated myocytes excluding contamination by other cell types. Using the specific Na(v) channel agonist veratridine and antagonist tetrodotoxin (TTX), we unmasked a contribution of these channels in the response to the depolarizing agent KCl on rat aortic isometric tension recorded from endothelium-denuded aortic rings. Experimental conditions excluded a contribution of Na(v) channels from the perivascular sympathetic nerve terminals. Addition of low concentrations of KCl (2-10 mM), which induced moderate membrane depolarization (e.g., from -55.9+/-1.4 mV to -45.9+/-1.2 mV at 10 mmol/L as measured with microelectrodes), triggered a contraction potentiated by veratridine (100 microM) and blocked by TTX (1 microM). KB-R7943, an inhibitor of the reverse mode of the Na(+)/Ca(2+) exchanger, mimicked the effect of TTX and had no additive effect in presence of TTX. CONCLUSIONS/SIGNIFICANCE: These results define a new role for Na(v) channels in arterial physiology, and suggest that the TTX-sensitive Na(v)1.2 isoform, together with the Na(+)/Ca(2+) exchanger, contributes to the contractile response of aortic myocytes at physiological range of membrane depolarization

Endothelin-Dependent Vasoconstriction in Human Uterine Artery: Application to Preeclampsia

BACKGROUND: Reduced uteroplacental perfusion, the initiating event in preeclampsia, is associated with enhanced endothelin-1 (ET-1) production which feeds the vasoconstriction of uterine artery. Whether the treatments of preeclampsia were effective on ET-1 induced contraction and could reverse placental ischemia is the question addressed in this study. We investigated the effect of antihypertensive drugs used in preeclampsia and of ET receptor antagonists on the contractile response to ET-1 on human uterine arteries. METHODOLOGY/PRINCIPAL FINDINGS: Experiments were performed, ex vivo, on human uterine artery samples obtained after hysterectomy. We studied variations in isometric tension of arterial rings in response to the vasoconstrictor ET-1 and evaluated the effects of various vasodilators and ET-receptor antagonists on this response. Among antihypertensive drugs, only dihydropyridines were effective in blocking and reversing the ET-1 contractile response. Their efficiency, independent of the concentration of ET-1, was only partial. Hydralazine, alpha-methyldopa and labetalol had no effect on ET-1 induced contraction which is mediated by both ET(A) and ET(B) receptors in uterine artery. ET receptors antagonists, BQ-123 and BQ-788, slightly reduced the amplitude of the response to ET-1. Combination of both antagonists was more efficient, but it was not possible to reverse the maximal ET-1-induced contraction with antagonists used alone or in combination. CONCLUSION: Pharmacological drugs currently used in the context of preeclampsia, do not reverse ET-1 induced contraction. Only dihydropyridines, which partially relax uterine artery previously contracted with ET-1, might offer interesting perspectives to improve placental perfusion

Les canaux sodiques voltage-dépendants dans la physiologie artérielle (implications fonctionnelles)

Les canaux sodiques voltage-dépendants (Nav) sont présents dans toutes les cellules excitables où ils sont responsables de l'initiation et la propagation des potentiels d'action. En 1988, l'enregistrement de courants sodiques voltage-dépendants (INa) dans les myocytes d'artères pulmonaires de lapin, traduisait la présence des Nav dans ce tissu duquel on les supposait absents compte tenu de leur physiologie et notamment, l'absence de potentiels d'action. Depuis la présence des courants INa a été confirmée dans les artères humaines et animales, sans qu'aucun rôle fonctionnel des Nav ne soit clairement défini. L'objectif de ce travail consistait à identifier les Nav présents dans les artères et à déterminer leur rôle physiologique dans ce tissu. Nous établissons, la présence d'isoformes a et b des Nav dans les tissus artériels humains et animaux avec certaines différences dans les profils d'expression. Ainsi, chez l'homme, plusieurs transcrits sont détectés dans les cellules musculaires lisses artérielles (CMLs) dont les isoformes neuronales Nav1.2, 1.3, 1.6 et l'isoforme cardiaque Nav1.5 ; Nav 1.3 étant majoritaire. Dans l'aorte de rat, si on détecte Nav1.2, 1.3, 1.5 et 1.6, seule Nav1.2 semble présente dans les CMLs, les autres étant vraisemblablement localisées au niveau de l'endothélium et des terminaisons nerveuses. Nous mettons également en évidence un rôle des Nav dans la contraction artérielle. Deux composantes sensibles à la tétrodotoxine (TTX), antagoniste spécifique des Nav, sont discriminées. La première correspond à l'activation de Nav présents au niveau des terminaisons nerveuses périvasculaires sympathiques. L'autre composante "musculaire lisse" révèle l'activation des Nav présents dans les CMLs et est démasquée par les dépolarisations modérées induites par de faibles concentrations en KCl. Une étude réalisée sur des modèles de rat hypertendus a permis de démontrer qu'une activité exacerbée de ces canaux pouvait être lourde de conséquences sur le tonus myogénique et donc impliquée dans l'hypertension. Nos résultats révèlent donc, pour la première fois, un rôle d'isoformes neuronales des Nav dans la physiologie artérielle. L'activité de ces canaux semble dépendante de l'état de dépolarisation ou d'hyperpolarisation des tissusVoltage-gated sodium channels (Nav) are presents in excitable cells where they are responsible for the initiation and propagation of action potentials. In 1988, the recording of voltage-gated sodium current (INa) in rabbit pulmonary artery myocytes shown the presence of Nav in this tissue. According to arterial physiology and particularly, absence of action potentials, INa was thought to be absent of the arterial tissue. Despite an increasing number of studies characterizing these Na+ currents in various arterial smooth muscle cells (ASMCs), there is still no information of whether or not these channels play a functional role in arteries. In the present work, we looked for an identification of the Nav and a potential role of Na+ channels activity in the control of aortic contraction. We established the presence of Nav a and b isoforms in human and animal arterial tissue with differences in expression profile. In human artery, several transcripts are detected in ASMCs: neuronal isoforms: Nav 1.2, Nav 1.3, Nav 1.6 and the cardiac one Nav 1.5; Nav 1.3 is predominant. In rat aorta, if several isoforms Nav 1.2, 1.3, 1.5 et 1.6 are detected, only Nav 1.2 appear to be present in ASMCs, the other isoforms would probably localized in the endothelium and nerve terminals. We evidenced a functional role of Na+ channels in the arterial contraction. Two different components highly sensitive to tetrodotoxin (TTX) were discriminated. First component match with the activation of Nav localized at perivascular sympathetic nerves terminals. The second one reveals the activation of Nav localized in ASMCs and is unmasked only after moderate depolarization by low KCl. A study realized on hypertensive rat models allowed demonstrating that an enhanced activity of these channels could have consequence on myogenic tone and so be involved in hypertension. Our results reveal, for the first time, a role for Nav neuronal isoforms in the arterial physiology. This channel activity seems to be dependant upon depolarisation or hyperpolarisation status of arterial tissueMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Ranolazine: An Old Drug with Emerging Potential; Lessons from Pre-Clinical and Clinical Investigations for Possible Repositioning

International audienceIschemic heart disease is a significant public health problem with high mortality and morbidity. Extensive scientific investigations from basic sciences to clinics revealed multilevel alterations from metabolic imbalance, altered electrophysiology, and defective Ca2+/Na+ homeostasis leading to lethal arrhythmias. Despite the recent identification of numerous molecular targets with potential therapeutic interest, a pragmatic observation on the current pharmacological R&D output confirms the lack of new therapeutic offers to patients. By contrast, from recent trials, molecules initially developed for other fields of application have shown cardiovascular benefits, as illustrated with some anti-diabetic agents, regardless of the presence or absence of diabetes, emphasizing the clear advantage of “old” drug repositioning. Ranolazine is approved as an antianginal agent and has a favorable overall safety profile. This drug, developed initially as a metabolic modulator, was also identified as an inhibitor of the cardiac late Na+ current, although it also blocks other ionic currents, including the hERG/Ikr K+ current. The latter actions have been involved in this drug’s antiarrhythmic effects, both on supraventricular and ventricular arrhythmias (VA). However, despite initial enthusiasm and promising development in the cardiovascular field, ranolazine is only authorized as a second-line treatment in patients with chronic angina pectoris, notwithstanding its antiarrhythmic properties. A plausible reason for this is the apparent difficulty in linking the clinical benefits to the multiple molecular actions of this drug. Here, we review ranolazine’s experimental and clinical knowledge on cardiac metabolism and arrhythmias. We also highlight advances in understanding novel effects on neurons, the vascular system, skeletal muscles, blood sugar control, and cancer, which may open the way to reposition this “old” drug alone or in combination with other medications

Dietary supplementation with a specific melon concentrate reverses vascular dysfunction induced by cafeteria diet

Background: Obesity-related metabolic syndrome is associated with high incidence of cardiovascular diseases partially consecutive to vascular dysfunction. Therapeutic strategies consisting of multidisciplinary interventions include nutritional approaches. Benefits of supplementation with a specific melon concentrate, enriched in superoxide dismutase (SOD), have previously been shown on the development of insulin resistance and inflammation in a nutritional hamster model of obesity. Objective: We further investigated arterial function in this animal model of metabolic syndrome and studied the effect of melon concentrate supplementation on arterial contractile activity. Design and results: The study was performed on a hamster model of diet-induced obesity. After a 15-week period of cafeteria diet, animals were supplemented during 4 weeks with a specific melon concentrate (Cucumis melo L.) Contractile responses of isolated aorta to various agonists and antagonists were studied ex vivo. Cafeteria diet induced vascular contractile dysfunction associated with morphological remodeling. Melon concentrate supplementation partially corrected these dysfunctions; reduced morphological alterations; and improved contractile function, especially by increasing nitric oxide bioavailability and expression of endogenous SOD. Conclusions: Supplementation with the specific melon concentrate improves vascular dysfunction associated with obesity. This beneficial effect may be accounted for by induction of endogenous antioxidant defense. Such an approach in line with nutritional interventions could be a useful strategy to manage metabolic syndrome–induced cardiovascular trouble

La supplémentation alimentaire avec un concentré spécifique de melon corrige la dysfonction vasculaire induite par un régime cafétéria

International audienceBackground: Obesity-related metabolic syndrome is associated with high incidence of cardiovascular diseases partially consecutive to vascular dysfunction. Therapeutic strategies consisting of multidisciplinary interventions include nutritional approaches. Benefits of supplementation with a specific melon concentrate, enriched in superoxide dismutase (SOD), have previously been shown on the development of insulin resistance and inflammation in a nutritional hamster model of obesity. Objective: We further investigated arterial function in this animal model of metabolic syndrome and studied the effect of melon concentrate supplementation on arterial contractile activity. Design and results: The study was performed on a hamster model of diet-induced obesity. After a 15-week period of cafeteria diet, animals were supplemented during 4 weeks with a specific melon concentrate (Cucumis melo L.) Contractile responses of isolated aorta to various agonists and antagonists were studied ex vivo. Cafeteria diet induced vascular contractile dysfunction associated with morphological remodeling. Melon concentrate supplementation partially corrected these dysfunctions; reduced morphological alterations ; and improved contractile function, especially by increasing nitric oxide bioavailability and expression of endogenous SOD. Conclusions: Supplementation with the specific melon concentrate improves vascular dysfunction associated with obesity. This beneficial effect may be accounted for by induction of endogenous antioxidant defense. Such an approach in line with nutritional interventions could be a useful strategy to manage metabolic syndromeÁinduced cardiovascular trouble

Hypoxic Conditions Promote Rhythmic Contractile Oscillations Mediated by Voltage-Gated Sodium Channels Activation in Human Arteries

International audienceArterial smooth muscle exhibits rhythmic oscillatory contractions called vasomotion and believed to be a protective mechanism against tissue hypoperfusion or hypoxia. Oscillations of vascular tone depend on voltage and follow oscillations of the membrane potential. Voltage-gated sodium channels (Nav), responsible for the initiation and propagation of action potentials in excitable cells, have also been evidenced both in animal and human vascular smooth muscle cells (SMCs). For example, they contribute to arterial contraction in rats, but their physiopathological relevance has not been established in human vessels. In the present study, we investigated the functional role of Nav in the human artery. Experiments were performed on human uterine arteries obtained after hysterectomy and on SMCs dissociated from these arteries. In SMCs, we recorded a tetrodotoxin (TTX)-sensitive and fast inactivating voltage-dependent INa current. Various Nav genes, encoding α-subunit isoforms sensitive (Nav 1.2; 1.3; 1.7) and resistant (Nav 1.5) to TTX, were detected both in arterial tissue and in SMCs. Nav channels immunostaining showed uniform distribution in SMCs and endothelial cells. On arterial tissue, we recorded variations of isometric tension, ex vivo, in response to various agonists and antagonists. In arterial rings placed under hypoxic conditions, the depolarizing agent KCl and veratridine, a specific Nav channels agonist, both induced a sustained contraction overlaid with rhythmic oscillations of tension. After suppression of sympathetic control either by blocking the release of catecholamine or by antagonizing the target adrenergic response, rhythmic activity persisted while the sustained contraction was abolished. This rhythmic activity of the arteries was suppressed by TTX but, in contrast, only attenuated by antagonists of calcium channels, Na+/Ca2+ exchanger, Na+/K+-ATPase and the cardiac Nav channel. These results highlight the role of Nav as a novel key element in the vasomotion of human arteries. Hypoxia promotes activation of Nav channels involved in the initiation of rhythmic oscillatory contractile activit

Antagonism of Nav channels and α1-adrenergic receptors contributes to vascular smooth muscle effects of ranolazine

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Terlipressin, a vasoactive prodrug recommended in hepatorenal syndrome, is an agonist of human V1, V2 and V1B receptors: Implications for its safety profile

International audienceTerlipressin is recommended as a gold standard to treat hepatorenal syndrome complicating liver cirrhosis. It is presented as a specific V1A receptor agonist, beyond its enzymatic conversion into lysine8-Vasopressin (LVP), able to counteract the splanchnic vasodilation. However, the complete pharmacological characterization of this drug with respect to the different vasopressin receptor subtypes is missing. We studied terlipressin intrinsic properties, focusing not only on V1A, but also on other vasopressin receptor subtypes. The experimental studies were conducted on rat and human cellular models. Binding experiments were performed on rat liver membranes and CHO cells transfected with the different human vasopressin receptor subtypes. Agonist status was assessed from inositol phosphate or cyclic AMP assays, and measurement of intracellular calcium variations, performed on cultured vascular smooth muscle cells from rat aorta and human uterine artery and CHO cells. Terlipressin binds to the rat and human V1A receptors with an affinity in the micromolar range, a value 120 fold lower than that of LVP. It induces a rapid and transient intracellular calcium increase, a robust stimulation of phospholipase C but with reduced maximal efficiencies as compared to LVP, indicating a partial V1A agonist property. In addition, terlipressin is also a full agonist of human V2 and V1B receptors, with also a micromomolar affinity