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It is supposed that TRPA1 receptor can be activated by hydrogen sulphide (H2S). Here, we have investigated the role of TRPA1 receptor in H2S-induced [Ca(2+)]i increase in trigeminal ganglia (TRG) neurons, and the involvement of capsaicin-sensitive sensory nerves in H2S-evoked cutaneous vasodilatation. [Ca(2+)]i was measured with ratiometric technique on TRG neurons of TRPA1(+/+) and TRPA1(-/-) mice after NaHS, Na2S, allylisothiocyanate (AITC) or KCl treatment. Microcirculatory changes in the ear were detected by laser Doppler imaging in response to topical NaHS, AITC, NaOH, NaSO3 or NaCl. Mice were either treated with resiniferatoxin (RTX), or CGRP antagonist BIBN4096, or NK1 receptor antagonist CP99994, or K(+) ATP channel blocker glibenclamide. Alpha-CGRP(-/-) and NK1 (-/-) mice were also investigated. NaHS and Na2S increased [Ca(2+)]i in TRG neurons derived from TRPA(+/+) but not from TRPA1(-/-) mice. NaHS increased cutaneous blood flow, while NaOH, NaSO3 and NaCl did not cause significant changes. NaHS-induced vasodilatation was reduced in RTX-treated animals, as well as by pre-treatment with BIBN4096 or CP99994 alone or in combination. NaHS-induced vasodilatation was significantly smaller in alpha-CGRP(-/-) or NK1 (-/-) mice compared to wild-types. H2S activates capsaicin-sensitive sensory nerves through TRPA1 receptors and the resultant vasodilatation is mediated by the release of vasoactive sensory neuropeptides CGRP and substance P.

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1IntroductionMagnesium and its alloys have ag reat potential for several industriala nd biomedical applications due to their non-toxicity and high strength-weight ratio, though their practical use is severely limited by their poor corrosion resistance in most aqueouse nvironments [1][2][3][4].I no rder to slow down this degradation, it is mandatory to gather precise knowledge about the mechanism of the process. Unfortunately,t he mechanism of magnesium corrosion remains controversial, and it presents certain uniquef eatures when compared to the corrosion of other active metals,i np articular with regard to the involvedh ydrogen evolution. While the main cathodic half-reaction leads to proton reduction into hydrogen gas,t his reaction has been recordedt oo ccur on magnesium not only under cathodic polarization, as expected, but also when increasing anodic overpotentials are applied to the material. This phenomenon, usually termed as the "Negative Dif-ferenceE ffect" [1,3],h as been traditionally invokedt o support the formationo fm agnesium (I) cationsa si ntermediate speciesd uring the degradation of this metal [ 1]. That is,o xidation of magnesium at the anodic sites would produceM g(I) species which subsequently react with water producing the hydrogeng as [1,5].Indeed, there are published reports suggesting that the apparent valence of the anodic half-reaction during the corrosiono fm agnesium was smaller than 2.0, which has been regarded the main evidence of the mechanism involvingu nivalent Mg cations [ 6].H owever, the advent of an ew rangeo fs ensitive microelectrochemical and spectroelectrochemical methods is delivering new experimental evidences that anodic dissolution produces solely Mg(II) instead, through a2 -electron exchange process [7][8][9][10][11].C oupling of electrochemicalm easurements with atomic emission spectroelectrochemistry supported that the apparentu nbalanceb etween Mg dissolution and hydrogenr elease rather arises from the formation of both soluble and insoluble Mg 2 + species, the latter increasing with the elapse of time,t hus effectively correlating to an n = 2m echanism [12].T his would relatet ot he formation of dark bi-layered film precipitates on anodicallyp olarised magnesium in chloride solutions [13][14][15][16],b ecause this film has been reported to exhibit enhancedc atalytic activity towards hydrogen evolution [15,17].T hese lattero bservations can be regardedm ore consistent with the expectation that no direct determination of the Mg(I) should be feasible due Abstract:S canning ElectrochemicalM icroscopy (SECM) is presented as an essential tool for the local characterization of the still uncertain mechanismf or magnesium corrosion. Ther eaction leading to magnesium release and hydrogen evolution from separated magnesium cathodes and anodes has been imaged using an adequate combination of the operation modes available in SECM. Magnesium ion selective microelectrodes (Mg-ISMEs) were used for the visualization of the heterogeneously distributed release of magnesium (II) spe...

Novel dual potentiometric microsensor probe has been developed for the simultaneous detection of Zn 2+ concentration and pH distributions in the Scanning Electrochemical Microscopy investigation of corroding galvanized steel. The individual sensors show nearly theoretical behavior over a wide concentration range. The applicability of this probe is first demonstrated on a Fe-Zn galvanic couple, as it shows excellent performance in these simultaneous model experiments. In addition, linear scans recorded over a cut edge of coated galvanized steel evidences the complementary information gathered on the electrochemical behavior of the corroding sample, and adumbrates promising and feasible applications of multi-barrel microelectrodes in corrosion research.