Hydrogen sulfide inhibits carbachol- induced contractile responses in β-escin permeabilized guinea-pig taenia caecum

Merve Denizalti, Nezahat Tugba Durlu-Kandilci, Turgut Emrah Bozkurt, Inci Sahin-Erdemli. Hacettepe University Faculty of Pharmacy Department of Pharmacology, Ankara, Turkey.

Hydrogen sulfide is an endogenous mediator producing a potent relaxation response in vascular and nonvascular smooth muscles. While ATP sensitive potassium channels are involved in this relaxant effect on vascular smooth muscles, the mechanism in other smooth muscles has not been revealed yet. Besides, reactive oxygen species (ROS) are reported to be responsible from hydrogen sulfide induced cytotoxicity1,2,3. We have studied how H2S affect carbachol contractions in permeabilized guinea pig (male, 350-400 g) taenia caecum. Strips of taenia caecum were mounted in a chamber filled with Krebs’ solution under 100 mg tension. Isometric contractions were recorded and expressed as % of 80 mM K+ evoked contractions. Data are mean±S.E.M. Statistics was done by ANOVA/Bonferroni. P<0.05 was accepted as significant. Strips were permeabilized with 80 μM β-escin for 30 min. After filling the intracellular stores with Ca2+, a further contraction was elicited by 50 μM carbachol (27.8±3.7 %, n = 12) that was decreased by hydrogen sulfide donor NaHS (3x10-4 M) (8.2±1.8 %, n = 6). This decrease in contraction was reversed by hydrogen peroxide scavenger catalase (24.1±3.9 %, n = 8) but not by superoxide scavenger superoxide dismutase (10.5±2,2 %, n = 7) or hydroxyl radical scavenger N-acetyl cysteine (12.5±0.6 %, n = 5). 1 μM SR Ca2+-ATPase pump inhibitor cyclopiazonic acid (CPA) decreased the carbachol contraction to 17.5±3.2 % (n = 5) which was further inhibited by hydrogen sulfide (7.8±2.3 %, n = 6). 1 μM mitochondrial blocker carbonyl cyanide p-trifluromethoxyphenylhydrazone (FCCP) decreased the carbachol contraction to 13.2±1.6 % (n = 6) and this was not additionally changed by hydrogen sulfide (16.2±4,1 %, n = 6). In conclusion, we may propose that hydrogen peroxide and intracellular calcium store mitochondria have a role in hydrogen sulfide-induced decrease in carbachol contractions in taenia caecum.

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2.Toxicology 2004;203:69–76.
3.Drug Metab.Rev. 2006;38(4):733-744.

Supported by Hacettepe University Research Center.