Involvement of RhoA-mediated Ca2+ sensitization in antigen-induced bronchial smooth muscle hyperresponsiveness in mice.
BACKGROUND
It has recently been suggested that RhoA plays an important role in the enhancement of the Ca2+ sensitization of smooth muscle contraction. In the present study, a participation of RhoA-mediated Ca2+ sensitization in the augmented bronchial smooth muscle (BSM) contraction in a murine model of allergic asthma was examined.


METHODS
Ovalbumin (OA)-sensitized BALB/c mice were repeatedly challenged with aerosolized OA and sacrificed 24 hours after the last antigen challenge. The contractility and RhoA protein expression of BSMs were measured by organ-bath technique and immunoblotting, respectively.


RESULTS
Repeated OA challenge to sensitized mice caused a BSM hyperresponsiveness to acetylcholine (ACh), but not to high K+-depolarization. In alpha-toxin-permeabilized BSMs, ACh induced a Ca2+ sensitization of contraction, which is sensitive to Clostridium botulinum C3 exoenzyme, indicating that RhoA is implicated in this Ca2+ sensitization. Interestingly, the ACh-induced, RhoA-mediated Ca2+ sensitization was significantly augmented in permeabilized BSMs of OA-challenged mice. Moreover, protein expression of RhoA was significantly increased in the hyperresponsive BSMs.


CONCLUSIONS
These findings suggest that the augmentation of Ca2+ sensitizing effect, probably via an up-regulation of RhoA protein, might be involved in the enhanced BSM contraction in antigen-induced airway hyperresponsiveness.
Chiba
Yoshihiko
Y
Department of Pharmacology, School of Pharmacy, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan. chiba@hoshi.ac.jp
Ueno
Ayako
A
Shinozaki
Koji
K
Takeyama
Hisao
H
Nakazawa
Shuji
S
Sakai
Hiroyasu
H
Misawa
Miwa
M
D000818:Animals; D001249:Asthma / Q000139:chemically induced / Q000378:metabolism*; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism*; D016535:Bronchial Hyperreactivity / Q000139:chemically induced / Q000378:metabolism*; D001985:Bronchial Provocation Tests; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000503:physiopathology*; D010047:Ovalbumin; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D010047:Ovalbumin; D020742:rhoA GTP-Binding Protein; D002118:Calcium