Excitatory cholinergic responses in mouse primary bronchial smooth muscle require both Ca entry via l-type Ca channels and store operated Ca entry via Orai channels.

Malfunctions in airway smooth muscle Ca-signalling leads to airway hyperresponsiveness in asthma and chronic obstructive pulmonary disease. Ca-release from intracellular stores is important in mediating agonist-induced contractions, but the role of influx via l-type Ca channels is controversial. We re-examined roles of the sarcoplasmic reticulum Ca store, refilling of this store via store-operated Ca entry (SOCE) and l-type Ca channel pathways on carbachol (CCh, 0.1-10 µM)-induced contractions of mouse bronchial rings and intracellular Ca signals of mouse bronchial myocytes. In tension experiments, the ryanodine receptor (RyR) blocker dantrolene (100 µM) reduced CCh-responses at all concentrations, with greater effects on sustained rather than initial components of contraction. 2-Aminoethoxydiphenyl borate (2-APB, 100 μM), in the presence of dantrolene, abolished CCh-responses, suggesting the sarcoplasmic reticulum Ca store is essential for contraction. The SOCE blocker GSK-7975A (10 µM) reduced CCh-contractions, with greater effects at higher (e.g. 3 and 10 µM) CCh concentrations. Nifedipine (1 µM), abolished remaining contractions in GSK-7975A (10 µM). A similar pattern was observed on intracellular Ca-responses to 0.3 µM CCh, where GSK-7975A (10 µM) substantially reduced Ca transients induced by CCh, and nifedipine (1 µM) abolished remaining responses. When nifedipine (1 µM) was applied alone it had less effect, reducing tension responses at all CCh concentrations by 25% - 50%, with greater effects at lower (e.g. 0.1 and 0.3 µM) CCh concentrations. When nifedipine (1 µM) was examined on the intracellular Ca-response to 0.3 µM CCh, it only modestly reduced Ca signals, while GSK-7975A (10 µM) abolished remaining responses. In conclusion, Ca-influx from both SOCE and l-type Ca channels contribute to excitatory cholinergic responses in mouse bronchi. The contribution of l-type Ca channels was especially pronounced at lower doses of CCh, or when SOCE was blocked. This suggests l-type Ca channels might be a potential target for bronchoconstriction under certain circumstances.