1999/06/01 by Akihiro Yoshii, Kunihiko Iizuka, Kunio Dobashi +4
paper · doi:10.1165/ajrcmb.20.6.3441
Abstract The mechanism of Ca2+ sensitization of contraction has not been elucidated in airway smooth muscle (SM). To determine the role of a small G protein, rhoA p21, and its target protein, rho-associated coiled coil–forming protein kinase (ROCK), in receptor-coupled Ca2+ sensitization of airway SM, we studied the effect of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a ROCK inhibitor, on isometric contractions in rabbit tracheal and human bronchial SM. Y-27632 completely reversed 1 μM carbachol (CCh)-induced contraction of intact trachea with a concentration producing half-maximum inhibition of effect (IC50) of 1.29 ± 0.2 μM (n = 5). Although 4β-phorbol 12,13-dibutyrate (1 μM)–induced Ca2+ sensitization was relatively resistant to Y-27632 in α-toxin–permeabilized trachea, CCh (100 μM) plus guanosine triphosphate (GTP) (3 μM)– and guanosine 5′-O-(3′-thiotriphosphate) (10 μM)–induced contractions were relaxed completely by Y-27632 with IC50 of 1.44 ± 0.3 (n = 6) and 1.15 ± 0.3 μM (n = 6). Endothelin-1 (1 μM) plus GTP (3 μM)– developed force was also reversed by Y-27632 with IC50 of 4.10 ± 1.1 μM (n = 6) in the α-toxin–permeabilized bronchus. Both the rabbit and human SM expressed rhoA p21, ROCK I, and its isoform ROCK II. Collectively, rho/ROCK–mediated Ca2+ sensitization plays a central role in the sustained phase of airway SM contraction, and selective inhibition of this pathway may become a new strategy to resolve airflow limitation in asthma.