Hydrogen sulphide‐induced relaxation of porcine peripheral bronchioles

Background and Purpose Hydrogen sulphide ( H 2 S ) is an endogenous gasotransmitter. Although it has been shown to elicit responses in vascular and other smooth muscle preparations, a role for endogenously produced H 2 S in mediating airway tone has yet to be demonstrated. Therefore, the aim of this study was to determine whether H 2 S is produced within the airways and to determine the functional effect on airway tone. Experimental Approach Small peripheral airways (<5 mm in diameter) from porcine lungs were set up in isolated tissue baths, pre‐contracted with the muscarinic agonist carbachol, and then exposed to either the H 2 S donor sodium hydrosulphide ( NaHS ), or the precursor L ‐cysteine. H 2 S production from L ‐cysteine or 3‐mercaptopyruvate in tissue homogenates was measured by the methylene blue assay. Expression of the H 2 S ‐synthesizing enzymes cystathionine β‐synthase ( CBS ), cystathionine γ lyase ( CSE ) and 3‐mercaptopyruvate sulphurtransferase (3‐ MST ) were measured by W estern blotting. Key Results NaHS caused a large relaxation of the airways, which was inhibited partially by pre‐contraction with KCl or exposure to tetraethylammonium, but not glibenclamide, paxilline or 4‐aminopyridine. L ‐cysteine also caused a relaxation of the airways which was inhibited by the CBS inhibitor aminooxyacetic acid. Tissue homogenates from airways exposed to L‐cysteine or 3‐mercaptopyruvate in vitro showed a significant production of H 2 S . W estern blotting demonstrated immunoreactivity to CBS , CSE and 3‐ MST enzymes in the airways. Conclusions and Implications These data demonstrate that H 2 S can be produced endogenously within porcine airways causing relaxation. The mechanism of relaxation depends, in part, on K + channel activity.