Site difference in RhoA expression between rat bronchial and tracheal smooth muscles after antigen challenge--relation to development of hyperresponsiveness.

Abstract

The present study compared the effects of repeated antigen exposure on the development of hyperresponsiveness and the expression of RhoA in the main bronchial and lower tracheal smooth muscles of sensitized Actively sensitized rats were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge the isometrical contractions of the bronchial and tracheal smooth muscles were measured. Immunoblottings were also performed using bronchial and tracheal homogenates and the density ratios of RhoA/beta-actin were calculated to quantify the levels of RhoA. Acetylcholine-induced contraction of bronchial, but not tracheal, smooth muscle of antigen-treated rats was significantly augmented as compared with that of control rats, indicating that airway hyperresponsiveness appeared by antigen challenge in bronchial smooth muscle. RhoA expression in bronchial, but not tracheal, smooth muscle was significantly increased in the antigen-treated animals. The increased expression of RhoA is suggested to have an important role in developing hyperresponsiveness of bronchial smooth muscle.