Hydrogen sulphide inhibits Ca 2+ release through InsP 3 receptors and relaxes airway smooth muscle

Key points•  The novel signalling molecule hydrogen sulphide (H 2 S) regulates diverse cell physiological processes in several organs and systems including airway smooth muscle contractility. •  We explored the mechanisms of H 2 S‐induced smooth muscle relaxation in small intrapulmonary airways using lung slices and imaging approaches. •  We found that exogenous and endogenous H 2 S inhibited intracellular Ca 2+ release specifically through the inositol‐1,4,5‐trisphosphate (InsP 3 ) receptor in smooth muscle cells and reversibly inhibited acetylcholine‐induced intracellular Ca 2+ oscillations, thus leading to airway dilatation. •  The effects of H 2 S on InsP 3 ‐induced Ca 2+ release and airway contraction were mimicked by the reducing agent dithiothreitol and inhibited by the oxidizing agent diamide, suggesting that H 2 S acts as a thiol‐reducing agent to reduce Ca 2+ release through InsP 3 receptors and to evoke relaxation. •  Our results suggest that endogenously produced H 2 S is a novel modulator of InsP 3 ‐mediated Ca 2+ signalling in airway smooth muscle and thus promotes bronchodilatation.Abstract  Hydrogen sulphide (H 2 S) is a signalling molecule that appears to regulate diverse cell physiological process in several organs and systems including vascular and airway smooth muscle cell (SMC) contraction. Decreases in endogenous H 2 S synthesis have been associated with the development of cardiovascular diseases and asthma. Here we investigated the mechanism of airway SMC relaxation induced by H 2 S in small intrapulmonary airways using mouse lung slices and confocal and phase‐contrast video microscopy. Exogenous H 2 S donor Na 2 S (100 μ m ) reversibly inhibited Ca 2+ release and airway contraction evoked by inositol‐1,4,5‐trisphosphate (InsP 3 ) uncaging in airway SMCs. Similarly, InsP 3 ‐evoked Ca 2+ release and contraction was inhibited by endogenous H 2 S precursor l ‐cysteine (10 m m ) but not by l‐ serine (10 m m ) or either amino acid in the presence of dl‐ propargylglycine (PPG). Consistent with the inhibition of Ca 2+ release through InsP 3 receptors (InsP 3 Rs), Na 2 S reversibly inhibited acetylcholine (ACh)‐induced Ca 2+ oscillations in airway SMCs. In addition, Na 2 S, the H 2 S donor GYY‐4137, and l‐ cysteine caused relaxation of airways pre‐contracted with either ACh or 5‐hydroxytryptamine (5‐HT). Na 2 S‐induced airway relaxation was resistant to a guanylyl cyclase inhibitor (ODQ) and a protein kinase G inhibitor (Rp‐8‐pCPT‐cGMPS). The effects of H 2 S on InsP 3 ‐evoked Ca 2+ release and contraction as well as on the relaxation of agonist‐contracted airways were mimicked by the thiol‐reducing agent dithiothreitol (DTT, 10 m m ) and inhibited by the oxidizing agent diamide (30 μ m ). These studies indicate that H 2 S causes airway SMC relaxation by inhibiting Ca 2+ release through InsP 3 Rs and consequent reduction of agonist‐induced Ca 2+ oscillations in SMCs. The results suggest a novel role for endogenously produced H 2 S that involves the modulation of InsP 3 ‐evoked Ca 2+ release – a cell‐signalling system of critical importance for many physiological and pathophysiological processes.