Role of endogenous hydrogen sulfide in nerve-evoked relaxation of pig terminal bronchioles

Abstract

Hydrogen sulfide (H₂S) is a gasotransmitter employed for intra- and inter-cellular communication in almost all organ systems. This study investigates the role of endogenous H₂S in nerve-evoked relaxation of pig terminal bronchioles with 260 μm medium internal lumen diameter. High expression of the H₂S synthesis enzyme cystathionine γ-lyase (CSE) in the bronchiolar muscle layer and strong CSE-immunoreactivity within nerve fibers distributed along smooth muscle bundles were observed. Further, endogenous H₂S generated in bronchiolar membranes was reduced by CSE inhibition. In contrast, cystathionine β-synthase expression, another H₂S synthesis enzyme, however was not consistently detected in the bronchiolar smooth muscle layer. Electrical field stimulation (EFS) and the H₂S donor P-(4-methoxyphenyl)-P-4-morpholinylphosphinodithioic acid (GYY4137) evoked smooth muscle relaxation. Inhibition of CSE, nitric oxide (NO) synthase, soluble guanylyl cyclase (sGC) and of ATP-dependent K⁺, transient receptor potential A1 (TRPA₁) and transient receptor potential vanilloid 1 (TRPV₁) channels reduced the EFS relaxation but failed to modify the GYY4137 response. Raising extracellular K⁺ concentration inhibited the GYY4137 relaxation. Large conductance Ca²⁺-activated K⁺ channel blockade reduced both EFS and GYY4137 responses. GYY4137 inhibited the contractions induced by histamine and reduced to a lesser extent the histamine-induced increases in intracellular [Ca²⁺]. These results suggest that relaxation induced by EFS in the pig terminal bronchioles partly involves the H₂S/CSE pathway. H₂S response is produced via NO/sGC-independent mechanisms involving K⁺ channels and intracellular Ca²⁺ desensitization-dependent pathways. Thus, based on our current results H₂S donors might be useful as bronchodilator agents for the treatment of lung diseases with persistent airflow limitation, such as asthma and chronic obstructive lung disease.

Keywords: Cystathionine β-synthase; Cystathionine γ-lyase; GYY4137; Hydrogen sulfide; Nerve-evoked relaxation; Pig terminal bronchioles.