Effects of hydrogen sulfide on relaxation responses in the lower esophageal sphincter in rabbits: the potential role of potassium channels

Hydrogen sulfide (H₂S) is a significant physiologic inhibitory neurotransmitter. The main goal of this research was to examine the contribution of diverse potassium (K⁺) channels and nitric oxide (NO) in mediating the H₂S effect on electrical field stimulation (EFS)-induced neurogenic contractile responses in the lower esophageal sphincter (LES). EFS-induced contractile responses of rabbit isolated LES strips were recorded using force transducers in organ baths that contain Krebs–Henseleit solutions (20 ml). Cumulative doses of NaHS, L-cysteine, PAG, and AOAA were evaluated in NO-dependent and NO-independent groups. The experiments were conducted again in the presence of K⁺ channel blockers. In both NO-dependent and NO-independent groups, NaHS, L-cysteine, PAG, and AOAA significantly reduced EFS-induced contractile responses. In the NO-dependent group, the effect of NaHS and L-cysteine decreased in the presence of 4-AP, and also the effect of NaHS decreased in the NO-dependent and independent group in the presence of TEA. In the NO-independent group, K⁺ channel blockers didn’t change L-cysteine-induced relaxations. K⁺ channel blockers had no impact on the effects of PAG and AOAA. In addition, NaHS significantly relaxed 80-mM KCl-induced contractions, whereas L-cysteine, PAG, and AOAA did not. In the present study, H₂S decreased the amplitudes of EFS-induced contraction responses. These results suggest that Kv channels and NO significantly contribute to exogenous H₂S and endogenous H₂S precursor L-cysteine inhibitory effect on lower esophageal sphincter smooth muscle.