[Analysis of airway hyperresponsiveness using in vitro contraction model].

We have established an in vitro model of airway hyperresponsiveness, using bovine tracheal smooth muscle cells (BTSMC)-embedded collagen gel lattice. When the gel was pretreated with lysophosphatidic acid (LPA), which activates small G-protein RhoA, ATP- and high K+ solution-induced gel contraction was significantly augmented. This was not due to the modulation of Ca(2+)-mobilizing properties, since ATP- and high K(+)-induced Ca2+ transients were not different significantly between control and LPA-treated BTSMC. Y-27632, an inhibitor of Rho-kinase, suppressed the LPA-induced augmentation of gel contraction, whereas it did not inhibit the contraction of control gels. Theophylline (> or = 1 microM) reversed the LPA-induced augmentation of gel contraction, whereas it inhibited control gel contraction only with a very high concentration (100 microM) Theophylline suppressed the LPA-induced membrane translocation of RhoA, indicating that it prevented airway hyperresponsiveness by inhibiting RhoA. We conclude from these results that theophylline inhibits LPA-induced, RhoA/Rho-kinase-mediated hyperresponsiveness of tracheal smooth muscle cells.