Repeated allergen inhalation induces phenotypic modulation of smooth muscle in bronchioles of sensitized rats

Repeated ovalbumin (OA) or saline exposure of sensitized Brown Norway rats was examined on agonist reactivity, airway smooth muscle (ASM) content, and contractile protein expression in small bronchioles at 24 h, 7 days, and 35 days after challenge. OA increased ASM content (P < 0.05 vs. saline) at 24 h, which resolved by 7 days. Maximum developed tension (Tmax) to carbachol, KCl, and 4-β-phorbol 12,13-dibutyrate was increased (P < 0.05) by OA in bronchioles at 24 h but was abrogated after correction for ASM. Differences in Tmaxwere not present at 7 days. In contrast, at 35 days, Tmaxwas increased (P < 0.05) after correction for ASM. Smooth muscle (sm)-α-actin, sm-myosin heavy chain (MHC) isoform 1, calponin, smoothelin-A, and sm-myosin light chain kinase expression were reduced (P < 0.05) by OA at 24 h in bronchioles but not in trachealis. Consistent with contraction findings, no difference in expression of these proteins was detected at 7 days. At 35 days, however, with the exception of sm-α-actin, their...