Abstract
H2S, synthesized endogenously from L‐cysteine via cystathionine‐γ‐lyase (CSE) and cystathionine‐β‐synthase (CBS), play a role in the regulation of gastrointestinal (GI) motility and secretion. Neither the expression of enzymes nor the mechanism of action of H2S in GI smooth muscle is fully known. Methods: Expression of CSE and CBS was analyzed by RT‐PCR and western blot. The effect of H2S on carbachol (CCh)‐induced Rho kinase activity and sustained contraction, and nitric oxide‐induced PDE5 activity, cGMP formation and muscle relaxation was examined using L‐cysteine (activator of CSE) or NaHS (H2S donor). Results: CSE, but not CBS was expressed in colonic smooth muscle cells of mouse, rabbit and human. CCh‐induced contraction in muscle strips and cells, and increased Rho kinase activity were inhibited by L‐cysteine and NaHS in a concentration‐dependent manner. Inhibition of Rho kinase activity and muscle contraction by L‐cysteine (but not NaHS) was blocked by CSE siRNA and CSE inhibitor, propargylglycine, respectively. L‐cysteine and NaHS also inhibited PDE5 activity, and augmented cGMP formation and muscle relaxation leading to increased (35%) colonic pellet propulsion. Conclusion: Activation of H2S‐producing CSE causes muscle relaxation via a dual mechanism involving inhibition of Rho kinase and PDE5 activity leading to downregulation of RhoA/Rho kinase pathway and upregulation of cGMP/PKG pathway.Grant Funding Source: DK‐28300
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