Rolle und Wirkungsmechanismus des Gasotransmitters Schwefelwasserstoff (H₂S) in der Kontrolle der kontraktilen Aktivität in der longitudinalen Muskulatur des Jejunums der Ratte

Abstract

After nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H₂S) was identified as the third »gasotransmitter« in the GI tract. Aim: To determine mechanisms of action of H₂S on contractile function in rat jejunum. Hypothesis: H₂S inhibits contractile activity via direct effects on smooth muscle. Methods: Jejunal longitudinal muscle strips (n = 6/rat) were obtained from 6 Lewis rats. We studied effects of NaHS (H₂S donor) on spontaneous and stimulated (bethanechol 3 × 10⁻⁶M) contractile activity and of L-cysteine (substrate for endogenous H₂S production) on spontaneous contractile activity. Propranolol, phentolamine, atropine, tetrodotoxin (TTX), capsaicin, L-N^G-nitro arginine (L-NNA), and glibenclamide (inhibitor of ATP-sensitive K⁺-channels) were evaluated, including L-cysteine without/with inhibitors of enzymatic H₂S production [aminooxyacetic acid (AOAA) and DL-propargylglycine (PPG)]. Electrical field stimulation (EFS) was studied in 6 other rats with selected inhibitors. Data are mean ± SEM change of baseline contractile activity in % (negative values: inhibition; positive values: stimulation). Immunohistochemistry of myenteric plexus was performed for H₂S-producing enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE). Results: NaHS (10⁻³ M) inhibited spontaneous and stimulated contractile activity (−43 ± 8 and −65 ± 6 % resp.; each p < 0.05); inhibitory effect was greater on stimulated activity (p < 0.05). Glibenclamide had no effect on response to NaHS on spontaneous contractile activity (−53 ± 10 vs −68 ± 6 % [with glibenclamide]; p = NS) but prevented in part inhibition of stimulated contractile activity by NaHS (−69 ± 9 vs −42 ± 7 % [with glibenclamide]; p = 0.005). All other antagonists (propranolol, phentolamine, atropine, TTX, capsaicin, and L-NNA) increased inhibitory effect of NaHS on spontaneous and stimulated contractile activity (p < 0.05). L-cysteine (10⁻² M) had no effect on contractile activity. Contractile responses to EFS at 50Hz under non-adrenergic, non-cholinergic conditions in combination with L-NNA and the VIP-antagonist were increased by AOAA and PPG (28 ± 34 vs 80 ± 39 %; p < 0.05). Immunohistochemistry showed both CBS and CSE in myenteric plexus. Conclusions: H₂S is an endogenous, inhibitory gasotransmitter in rat jejunum with direct effects on smooth muscle mediated partially by ATP-sensitive K⁺-channels. Intact neuromuscular transmission prevents the inhibitory effect of H₂S. Support: DFG KA 2329/1-1.