Pharmacological Actions of L‐cysteine on Isolated Bovine Irides

Abstract

PurposeTo investigate the pharmacological actions of L‐cysteine, a substrate for hydrogen sulfide (H2S) production on isolated bovine irides.MethodsIsolated bovine iris muscle strips were set up in organ baths containing oxygenated Krebs buffer (pH 7.4) at 37□ C. Changes in isometric tension were recorded via grass FT03 Force‐displacement transducers and analyzed using PolyView software. The relaxant action of L‐cysteine on basal and carbachol‐induced tone was studied in the presence or absence of enzyme inhibitors of the biosynthetic pathways for H2S and prostanoids.ResultsL‐cysteine (0.1 nM –100 μM) elicited a concentration‐dependent relaxation of basal and carbachol‐induced tone in bovine irides. In contrast, L‐cysteine had no relaxant effect on basal tone in porcine irides. Inhibition of cyclooxygenase with flurbiprofen (3 μM) had no significant effect on relaxation induced by L‐cysteine. The inhibitor of cystathionine β‐synthase, aminooxyacetic acid (30 μM) significantly (p<0.02) reduced the relaxation induced by L‐cysteine.ConclusionL‐cysteine can relax isolated bovine irides, an effect that is dependent on intramural biosynthesis of H2S. Prostanoids are not involved on this relaxant effect. Bovine irides appear to be more sensitive to the inhibitory action of L‐cysteine than its porcine counterpart, indicating that species differences exist in the response to this substrate.