Ca(2+)-signaling in airway smooth muscle cells is altered in T-bet knock-out mice

BACKGROUND: Airway smooth muscle cells (ASMC) play a key role in bronchial hyperresponsiveness (BHR). A major component of the signaling cascade leading to ASMC contraction is calcium. So far, agonist-induced Ca(2+)-signaling in asthma has been studied by comparing innate properties of inbred rat or mouse strains, or by using selected mediators known to be involved in asthma. T-bet knock-out (KO) mice show key features of allergic asthma such as a shift towards T(H)2-lymphocytes and display a broad spectrum of asthma-like histological and functional characteristics. In this study, we aimed at investigating whether Ca(2+)-homeostasis of ASMC is altered in T-bet KO-mice as an experimental model of asthma. METHODS: Lung slices of 100 to 200 μm thickness were obtained from T-bet KO- and wild-type mice. Airway contraction in response to acetylcholine (ACH) was measured by video-microscopy and Ca(2+)-signaling in single ASMC of lung slices was assessed using two-photon-microscopy. RESULTS: Airways from T-bet KO-mice showed increased baseline airway tone (BAT) and BHR compared to wild-type mice. This could be mimicked by incubation of lung slices from wild-type mice with IL-13. The increased BAT was correlated with an increased incidence of spontaneous changes in intracellular Ca(2+)-concentrations, whereas BHR correlated with higher ACH-induced Ca(2+)-transients and an increased proportion of ASMC showing Ca(2+)-oscillations. Emptying intracellular Ca(2+)-stores using caffeine or cyclopiazonic acid induced higher Ca(2+)-elevations in ASMC from T-bet KO- compared to wild-type mice. CONCLUSION: Altered Ca(2+)-homeostasis of ASMC contributes to increased BAT and BHR in lung slices from T-bet KO-mice as a murine asthma model. We propose that a higher Ca(2+)-content of the intracellular Ca(2+)-stores is involved in the pathophysiology of these changes.