Mechanisms of Action of the Gasotransmitter Hydrogen Sulfide in Modulating Contractile Activity of Longitudinal Muscle of Rat Ileum

Aim: This study aims to determine mechanisms of action of the gasotransmitter hydrogen sulfide (H₂S) on contractile activity in longitudinal muscle of rat ileum. Methods: Ileal longitudinal muscle strips were prepared to measure isometric contractions. Effects of sodium hydrosulfide (NaHS), a donor of H₂S, were evaluated on spontaneous contractile activity and after enhanced contractile activity with bethanechol. l-cysteine was evaluated as a potential endogenous donor of H₂S. We evaluated involvement of extrinsic nerves, enteric nervous system, visceral afferent nerves, nitric oxide, and K_ATP⁺ channel and K_Ca⁺ channel activity on the action of H₂S using non-adrenergic/non-cholinergic conditions, tetrodotoxin, capsaicin, l-N^G-nitro arginine (l-NNA), glibenclamide, and apamin, respectively, as well as electrical field stimulation. Result: NaHS dose-dependently and reversibly inhibited spontaneous and bethanechol-stimulated contractile activity (p < 0.05). l-cysteine had no inhibitory effect. Non-adrenergic/non-cholinergic conditions, tetrodotoxin, capsaicin, l-NNA, glibenclamide, or apamin had no major effect on total contractile activity by NaHS, although both tetrodotoxin and apamin decreased the frequency of bethanechol-enhanced contractile activity (p < 0.05). We could not demonstrate H₂S release by electrical field stimulation but did show that inhibition of cystathionine β synthase, an endogenous source of H₂S, augmented the inhibitory effect of low-frequency electrical field stimulation. Conclusion: H₂S inhibits contractile activity of ileal longitudinal muscle dose-dependently but not through pathways mediated by the extrinsic or enteric nervous system, visceral afferent nerves, nitric oxide, K_ATP⁺ channels, or K_Ca⁺ channels.