Abstract
Background/Aim: H<sub>2</sub>S is a novel vasoactivator. To verify the hypothesis that H<sub>2</sub>S may act as an endothelium-derived hyperpolarizing factor (EDHF) in the rat cerebrovasculature, the role of H<sub>2</sub>S in endothelium-derived relaxing factor (EDRF)-mediated responses was investigated. Methods: Cystathionine-γ-lyase (CSE) was knocked down with an siRNA technique. Artery diameter, hyperpolarization and Ca<sup>2+</sup>-activated K<sup>+</sup> (K<sub>Ca</sub>) current were measured. Results: CSE knockdown was indicated by a decrease in protein and mRNA expression in the rat middle cerebral artery (MCA) and cerebral basilar artery (CBA). Acetylcholine (ACh) induced significant hyperpolarization and vasodilation in endothelium-intact MCA and CBA. Removal of the endothelium abolished these responses. The nitric oxide (NO) synthase inhibitor <smlcap>L</smlcap>-NAME, but not the PGI<sub>2</sub> production inhibitor indomethacin, significantly inhibited ACh-induced hyperpolarization and vasodilation in the CBA. In the presence of <smlcap>L</smlcap>-NAME and indomethacin, ACh-induced hyperpolarization and vasodilation in the MCA and CBA were attenuated. The non-NO/PGI<sub>2</sub>-mediated responses were abolished by the K<sub>Ca</sub> channel blockers charybdotoxin and apamin. In the cerebral arteries from the CSE knockdown rat, non-NO/PGI<sub>2</sub>-mediated responses were significantly attenuated, and the remaining responses were abolished by charybdotoxin and apamin or the CSE inhibitor propargylglycine. CSE knockdown did not affect <smlcap>L</smlcap>-NAME-sensitive responses in the CBA. Sodium hydrosulfide (NaHS) augmented the K<sub>Ca</sub> current in CBA vascular smooth muscle cells. Conclusion: EDHF-mediated responses in rat cerebral arteries were due to H<sub>2</sub>S activating the K<sub>Ca</sub> channel.
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