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S. E. Ohia, C. A. Opere, E. M. Monjok, G. E. Kouamou, M. A. McKoy; Role of Hydrogen Sulfide in L-Cysteine Induced Relaxations of Isolated Porcine Irides. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3945.
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We have evidence that hydrogen sulfide (H2S) donors such as sodium hydrosulfide (NaHS) can produce relaxations of porcine iris smooth muscles and that this effect is partly mediated through KATP channels (Monjok et al., IOVS 46: E-Abstract 3684, 2005.). In the present study, we investigated the direct relaxant effect of L-cysteine, a substrate for the production of H2S from the enzymatic actions of cystathionine γ-lyase and cystathionine ß-synthase on carbachol-induced contractions in isolated porcine irides. Furthermore, we studied the role of H2S and prostanoids in the effects caused by L-cysteine in this tissue.
Isolated porcine iris muscle strips were set up in organ bathscontaining oxygenated Krebs buffer solution at 37oC. Longitudinal isometric tension was recorded via a grass FT03 Force-displacement Transducers and analyzed using the PolyView computer software. An initial load of 150 mg was placed on each tissue after which they were allowed to equilibrate for one hour. The relaxant action of L-cysteine on carbachol-induced tone was studied in the absence and presence of inhibitors of cystathionine γ -lyase (propargylglycine, PAG) and cystathionine ß-synthase (aminooxyacetic acid, AOA) and cyclooxygenase (flubiprofen).
L-cysteine (30 nM - 1 mM) produced concentration-dependent relaxations of carbachol-induced tone. Inhibition of cyclo-oxygenase with flurbiprofen (3 µM) produced significant (P < 0.001) enhancement of relaxations induced by L-cysteine. The inhibitor of cystathionine γ-lyase, PAG (1 mM) blocked relaxations caused by high concentrations of L-cysteine (> 100 µM). Interestingly, the inhibitor of cystathionine ß-synthase, AOA (30 µM) caused significant (P < 0.001) rightward shifts in the concentration-response curves to L-cysteine and attenuated the maximum inhibitory response.
The observed inhibitory action of L-cysteine in isolated porcine irides is dependent on endogenous biosynthesis of H2S by cystathionine γ-lyase and cystathionine ß-synthase. Furthermore, prostanoids are involved in the inhibitory action of L-cysteine in this tissue.
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