Airway hyperresponsiveness:: From molecules to bedside -: Selected contribution:: Airway contractility and smooth muscle Ca2+ signaling in lung slices from different mouse strains

To investigate the hypothesis that altered Ca2+ signaling in airway smooth muscle cells (SMCs) is responsible for airway hyperreactivity, we compared, with the use of confocal and phase-contrast microscopy, the airway contractility and Ca2+ changes in SMCs induced by acetylcholine (ACh) in lung slices from different mouse strains (A/J, Balb/C, and C3H/ HeJ). The airways from each mouse strain displayed a concentration-dependent contraction to ACh. The contractile response of the airways of the C3H/ HeJ mice was found, in contrast to earlier studies, to be much greater and faster than that of A/J and Balb/C mice. This difference in airway reactivity can be, in part, attributable to halothane, a volatile anesthetic that was previously used during in vivo measurements of airway reactivity but found here to significantly alter the ACh contractile response of airways in lung slices. The ACh-induced Ca2+ response of the airway SMCs in all of the various mouse strains was also concentration dependent. The magnitude of the initial Ca2+ increase and the frequency of the subsequent Ca2+ oscillations induced by ACh increased with ACh concentration. However, no differences in the Ca2+ responses to ACh could be distinguished between the mouse strains. These results suggest that the mechanism responsible for airway hyperreactivity in different mouse strains resides with the Ca2+ sensitivity of the contractile apparatus of the SMCs rather than with the Ca2+ signaling itself.