Relaxation of Porcine Bronchioles by Hydrogen Sulphide

Samia Rashid, Steve Alexander, Richard Roberts. University of Nottingham, Nottingham, UK

Hydrogen sulphide (H2S) is one of the three putative gasotransmitters. H2S is synthesised in vivo via the enzymes cystathionine γ lyase (CSE) and cystathionine β synthase (CBS) (Li et al., 2011). It has a wide variety of effects within the body, particularly within the vasculature. A role for endogenously-produced H2S in mediating airway tone has yet to be demonstrated. Therefore, the aim of this study was to determine whether H2S is produced within the airways and, if so, to determine the functional effect on airway tone.

Small peripheral airways (<5mm in diameter) from porcine lungs obtained from a local abattoir were mounted in isolated tissue baths in Krebs-Henseleit buffer gassed with 95% O2, 5% CO2. After pre-contraction with the muscarinic agonist carbachol, tissues were exposed to either the H2S donor NaHS, or the pre-cursor L-cysteine. H2S production from L-cysteine in tissue homogenates was measured using a biochemical assay (Abe & Kimura, 1996). Western blotting was used to detect the presence of CSE and CBS enzymes in homogenates of porcine airways.

Figure 1. A typical trace showing the effect of NaHS on bronchiole tone after contraction with the muscarinic agonist carbachol (CCh)

NaHS (1x10-3 M) caused a large, concentration-dependent relaxation of the airways (90 ± 7 % of the carbachol-induced contraction, n = 8, see figure 1). L-cysteine (1x10-3 M) caused a slow relaxation of the airways (40 ± 25 %, n = 7) which was inhibited by aminooxyacetic acid (1x10-4M) and propargylglycine (1x10-4M), inhibitors of CBS and CSE respectively. In tissue homogenates exposed to L-cysteine, there was a linear, time-dependent increase in H2S production over basal levels, (17.8 ± 3.4 nmole/mg protein at120 min). Western blotting demonstrated immunoreactivity to CBS but not the CSE enzyme in small peripheral bronchioles.

These data demonstrate that H2S is produced endogenously within porcine airways causing relaxation. Western blotting indicates that one of the enzymes required for the endogenous production of H2S, namely CBS, is present in the small peripheral airways. These data demonstrate a functional role for H2S in the airways, which may play a role in the pathology of airway diseases such as asthma and COPD.

Abe K. & Kimura H. (1996). J. Neurochem., 16, 1066-1071.

Li L., Rose P., & Moore P. K. (2011). Annu. Rev. Pharmacol. Toxicol., 51, 169-187.