Objective: To obtain information on the activation pathway of the monomeric G protein, RhoA, in bronchial smooth muscle, the expression of G alpha12 and G alpha13 in bronchial smooth muscle of the rat was determined. The levels of these G proteins were also compared between antigen-induced airway hyperresponsive and normal control groups.
Methods: Actively sensitized rats were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge, membrane preparations of bronchial smooth muscles were prepared. Immunoblottings were performed, and the density ratios of G alpha12/beta-actin and G alpha13/beta-actin were calculated to quantify the levels of these G-protein alpha subunits.
Results: Both G alpha12 and G alpha13 proteins were expressed in rat bronchial smooth muscle. The levels of bronchial G alpha12 and G alpha13 proteins in the repeatedly antigen challenged rats were significantly increased as compared with those in control animals; the magnitude of upregulation in the airway-hyperresponsive group was 89% and 68% in the control group, respectively.
Conclusion: G alpha12 and G alpha13 proteins were expressed in rat bronchial smooth muscle. Considering the probable involvement of G12 and G13 proteins in Ca2+ sensitization through Rho protein, the augmented expression of such G proteins after repeated antigen challenge may be responsible for the hyperresponsiveness of bronchial smooth muscle contraction in rats.