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

Hydrogen sulfide (HS) 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 HS 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, HS decreased the amplitudes of EFS-induced contraction responses. These results suggest that Kv channels and NO significantly contribute to exogenous HS and endogenous HS precursor L-cysteine inhibitory effect on lower esophageal sphincter smooth muscle.