Increased expression of G12 and G13 proteins in bronchial smooth muscle of airway hyperresponsive rats

Abstract:

Objective: To obtain information on the activation pathway of the monomeric G protein, RhoA, in bronchial smooth muscle, the expression of Gα ₁₂ and Gα ₁₃ 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 Gα ₁₂/β-actin and Gα ₁₃/β-actin were calculated to quantify the levels of these G-protein α subunits.¶Results: Both Gα ₁₂ and Gα ₁₃ proteins were expressed in rat bronchial smooth muscle. The levels of bronchial Gα ₁₂ and Gα ₁₃ 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: Gα ₁₂ and Gα ₁₃ 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.