Ca2+-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 Ca2+-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 Ca2+-homeostasis of ASMC
is altered in T-bet KO-mice as an experimental model of asthma.
Methods: Lung slices of 100 to 200 mu m thickness were obtained
from T-bet KO- and wild-type mice. Airway contraction in response
to acetylcholine (ACH) was measured by video-microscopy and
Ca2+-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
Ca2+-concentrations, whereas BHR correlated with higher ACH-induced
Ca2+-transients and an increased proportion of ASMC showing
Ca2+-oscillations. Emptying intracellular Ca2+-stores using
caffeine or cyclopiazonic acid induced higher Ca2+-elevations in
ASMC from T-bet KO- compared to wild-type mice. Conclusion: Altered
Ca2+-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 Ca2+-content of the intracellular Ca2+-stores is
involved in the pathophysiology of these changes.