Augmented acetylcholine‐induced, Rho‐mediated Ca²⁺ sensitization of bronchial smooth muscle contraction in antigen‐induced airway hyperresponsive rats

Abstract

Treatment with acetylcholine (ACh) of a b-escin-permeabilized intrapulmonary bronchial smooth muscle of the rat induced force when the Ca 2+ concentration was clamped at 1 mM. The AChinduced Ca 2+ sensitization of myo®laments was signi®cantly greater in antigen-induced airway hyperresponsive rats than in control rats. The ACh-induced Ca 2+ sensitization was completely blocked by treatment with Clostridium botulinum C3 exoenzyme, an inactivator of Rho family of proteins. Moreover, the protein level of RhoA in the intrapulmonary bronchi was signi®cantly increased in the airway hyperresponsive rats. Thus, increased airway smooth muscle contractility observed in asthmatics may be related to augmented agonist-induced, Rho-mediated Ca 2+ sensitization of myo®laments.

Upregulation of rhoA mRNA in Bronchial Smooth Muscle of Antigen-induced Airway Hyperresponsive Rats.

“…Similarly, an increased responsiveness of bronchial smooth muscle has been demonstrated in a rat model of AHR induced by repeated antigen inhalation (Chiba and Misawa, 1995a, b). In AHR rats, it has also been demonstrated that acetylcholine-induced RhoA-mediated Ca 2+ sensitization is markedly augmented concomitantly with an increased expression of RhoA protein in the bronchial smooth muscle (Chiba et al, 1999b). It is thus possible that the upregulation of RhoA protein in airway smooth muscle might be an essential event in the pathogenesis of AHR.…”

“…Male Wistar rats (6 weeks of age, specific pathogen-free, 170-190 g, Charles River Japan, Inc.) were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen (DNP-Asc) by the method described in our previous papers (Chiba & Misawa, 1995a,b;Chiba et al, 1999b). Age-matched non-sensitized normal animals were used as controls (Chiba and Misawa, 1995a,b;Chiba et al, 1999b).…”

“…Age-matched non-sensitized normal animals were used as controls (Chiba and Misawa, 1995a,b;Chiba et al, 1999b).…”

“…Recently, additional mechanisms have been suggested in agonist-induced smooth muscle contraction as a result of studies which used the simultaneous measurement of force development and intracellular Ca 2+ concentration, as well as those on various smooth muscle preparations which have been chemically permeabilized. It has been demonstrated that agonist stimulation increases myofilament Ca 2+ sensitivity in β-escin-permeabilized smooth muscle of the rat coronary artery (Satoh et al, 1994), guinea pig vas deferens (Fujita et al, 1995), canine trachea (Bremerich et al, 1997) and rat bronchus (Chiba et al, 1999b). Although the detailed mechanism is not fully understood, many investigators have suggested the participation of RhoA, a monomeric GTP binding protein, in the agonist-induced Ca 2+ sensitization (e.g., Fujita et al, 1995;Gong et al, 1997;Chiba et al, 1999b).…”

Mfge8 suppresses airway hyperresponsiveness in asthma by regulating smooth muscle contraction

“…Cytokines enhance ASM calcium sensitivity and contraction through a signaling pathway involving NF-κB, ras homolog gene family, member A (RhoA), and ROCK2 (2)(3)(4). Activation of this pathway leads to phosphorylation and inactivation of MLC phosphatase (MLCP) by ROCK2 (4,7,8).…”