| Summary: | Hydrogen sulfide (H2S) is a major physiologic gastrotransmitter. Its role in the regulation of the lower esophageal sphincter (LES) function remains unknown. The present study addresses this question.
Methods: Isometric contraction was monitored in circular smooth muscle strips of porcine LES. Changes in cytosolic Ca2+ concentration ([Ca2+]i) and force were simultaneously monitored in fura-2-loaded strips with front-surface fluorometry. The contribution of endogenous H2S to LES contractility was investigated by examining the effects of inhibitors of H2S-generating enzymes, including cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase, on the LES function.
Results: Porcine LES strips myogenically maintained a tetrodotoxin-resistant basal tone. Application of AOA (cystathionine-β-synthase inhibitor) or L-aspartic acid (L-Asp; 3-mercaptopyruvate sulfurtransferase inhibitor) but not DL-PAG (cystathionine-γ-lyase inhibitor), decreased this basal tone. The relaxant effects of AOA and L-Asp were additive. Maximum relaxation was obtained by combination of 1 mM AOA and 3 mM L-Asp. Immunohistochemical analyses revealed that cystathionine-β-synthase and 3-mercaptopyruvate sulfurtransferase, but not cystathionine-γ-lyase, were expressed in porcine LES. AOA+L-Asp–induced relaxation was accompanied by a decrease in [Ca2+]i and inversely correlated with the extracellular Na+ concentration ([Na+]o) (25-137.4 mM), indicating involvement of an Na+/Ca2+ exchanger. The reduction in the basal [Ca2+]i level by AOA was significantly augmented in the antral smooth muscle sheets of Na+/Ca2+ exchanger transgenic mice compared with wild-type mice.
Conclusions: Endogenous H2S regulates the LES myogenic tone by maintaining the basal [Ca2+]i via Na+/Ca2+ exchanger. H2S-generating enzymes may be a potential therapeutic target for esophageal motility disorders, such as achalasia.
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