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Our objective was to investigate whether pro-oxidant properties of ascorbic acid (AA) and tetrahydrobiopterin (BH(4)) modulate endothelium-dependent, electrotonically mediated arterial relaxation.In studies with rabbit iliac artery (RIA) rings, NO-independent, endothelium-derived hyperpolarizing factor (EDHF)-type relaxations evoked by the sarcoplasmic endoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid and the G protein-coupled agonist acetylcholine (ACh) were enhanced by AA (1 mM) and BH(4) (200 microM), which generated buffer concentrations of H(2)O(2) in the range of 40-80 microM. Exogenous H(2)O(2) potentiated cyclopiazonic acid (CPA)- and ACh-evoked relaxations with a threshold of 10-30 microM, and potentiation by AA and BH(4) was abolished by catalase, which destroyed H(2)O(2) generated by oxidation of these agents in the organ chamber. Adventitial application of H(2)O(2) also enhanced EDHF-type dilator responses evoked by CPA and ACh in RIA segments perfused intraluminally with H(2)O(2)-free buffer, albeit with reduced efficacy. In RIA rings, both control relaxations and their potentiation by H(2)O(2) were overcome by blockade of gap junctions by connexin-mimetic peptides (YDKSFPISHVR and SRPTEK) targeted to the first and second extracellular loops of the dominant vascular connexins expressed in the RIA. Superoxide dismutase attenuated the potentiation of EDHF-type relaxations by BH(4), but not AA, consistent with findings demonstrating a differential role for superoxide anions in the generation of H(2)O(2) by the two agents.Pro-oxidant effects of AA and BH(4) can enhance the EDHF phenomenon by generating H(2)O(2), which has previously been shown to amplify electrotonic hyperpolarization-mediated relaxation by facilitating Ca(2+) release from endothelial stores.

The TWIK related K+ channel TREK1 is an important member of the class of two-pore-domain K+ channels. It is a background K+ channel and is regulated by hormones, neurotransmitters, intracellular pH and mechanical stretch. This work shows that TREK1 is present both in mesenteric resistance arteries and in skin microvessels. It is particularly well expressed in endothelial cells. Deletion of TREK1 in mice leads to an important alteration in vasodilation of mesenteric arteries induced by acetylcholine and bradykinin. Iontophoretic delivery of acetylcholine and bradykinin in the skin of TREK1+/+ and TREK1−/− mice also shows the important role of TREK1 in cutaneous endothelium-dependent vasodilation. The vasodilator response to local pressure application is also markedly decreased in TREK1−/− mice, mimicking the decreased response to pressure observed in diabetes. Deletion of TREK1 is associated with a marked alteration in the efficacy of the G-protein-coupled receptor-associated cascade producing NO that leads to major endothelial dysfunction.

The existence of a cutaneous pressure-induced vasodilation (PIV) has recently been reported. This paper proposes a signal processing methodology to improve PIV knowledge. Temporal variations of laser Doppler signals rhythmic activities are first analyzed on anesthetized rats. The results lead to a method that provides a better PIV understanding.

L’etude menee sur des arteres iliaques de lapin montees sur myographe montre que l’AA (1 mmol/L) et BH4 (200 μmol/L) augmentent la relaxation de type EDHF induite par l’acide cyclopiazonique (CPA) inhibiteur SERCA et l’acetylcholine (ACh) un agoniste de la proteine G. Cet effet potentialisateur est abolit en presence de catalase sous-tendant un role du peroxyde d’hydrogene (H2O2). En effet, la methode de dosage amplex-red/HRP confirme la generation d’H2O2 par l’oxydation de l’AA et de BH4. D’autre part, l’ajout dans le bain d’incubation d’H2O2 exogene a dose similaire de l’H2O2 produit par l’oxydation de l’AA et BH4 mime l’action potentialisatrice de ces deux substances. Contrairement a l’AA, en presence de superoxyde dismutase, la formation d’H2O2 par BH4 est diminuee. Le DTPA, un chelateur de metaux permet de diminuer la production d’H2O2 par l’AA. Ceci indique que la generation d’H2O2 est liee principalement a la presence de l’anion superoxyde pour BH4 tandis que pour l’AA elle depend plus des traces de metaux. Le blocage des gap jonctions par l’utilisation de peptides mimetiques des connexines inhibe a la fois les relaxations temoins et potentialisees confirmant la nature electrotonique du phenomene EDHF dans chacun des cas. De nombreuses etudes ont rapporte l’effet benefique des proprietes anti-oxydantes de l’AA et de BH4 sur la relaxation NOdependante. Nos resultats montrent que les effets pro-oxydant de ces substances peuvent eux aussi ameliorer les dysfonctions vasculaires en generant de l’H2O2 par l’oxydation de l’AA catalyse par des metaux et l’autoxydation de BH4. En effet, lorsque la synthese de NO est inhibee de facon pharmacologique, l’oxydation de ces agents conduit a la formation d’H2O2 amplifiant la relaxation arterielle de type EDHF. La production d’H2O2 a partir du peroxyde est habituellement attenuee par le NO donnant le peroxynitrite, en competition avec la superoxyde dismutase. Il est donc possible qu’en cas de stress oxydatif important, caracterisant de nombreuses pathologies vasculaires, le phenomene EDHF soit potentialise pour contrebalancer la reduction de biodisponibilite du NO.