Calcium sensitization by the RhoA/Rho-kinase (ROCK) pathway contributes to the contraction in smooth muscle. Contractile stimuli can sensitize myosin to Ca2+ by activating RhoA/Rho-kinase that inhibits myosin light chain phosphatase activity. The present study was aimed at investigating the possible involvement of RhoA/Rho-kinase pathway in contractile responses to agonist (phenylephrine) and depolarizing (KCl) of mouse lung parenchymal tissues. Also, we investigated the effect of ethanol on RhoA/Rho-kinase pathway. Phenylephrine (10(-8)-10(-4) M) and KCl (10-80 mM) induced sustained contractions in parenchymal strips. Ethanol significantly attenuated the contractions to phenylephrine and KCl. The Rho-kinase inhibitors fasudil (5 x 10(-5) M) and Y-27632 (5 x 10(-5) M) inhibited contractions to in both control and ethanol-treated parenchymal strips. In addition, the relaxations induced by fasudil (10 4 M) and Y-27632 (5 x 10(-4) M) on parenchymal strips contracted by phenylephrine but not KCl was decreased in ethanol-treatment group. Also, RhoA, ROCK1 and ROCK2 expressions were detected in mouse lung parenchymal tissue. In ethanol-treated group, expression of RhoA and ROCK1 but not ROCK2 decreased compared to control. Furthermore, ethanol causes apoptotic changes in alveolar type I epithelial cells of parenchymal tissue. These results suggest that RhoA/Rho-kinase signaling pathway plays an important role in phenylephrine- and KCl-induced Ca2+ sensitization in mouse lung parenchymal tissue. Also, ethanol may be decrease phenylephrine- and KCl-induced contraction due to lowering the RhoA/Rhokinase-mediated Ca2+-sensitizing by inhibiting RhoA/Rho-kinase pathway in parenchymal tissue. These results may be lead to important insights into the mechanisms of lung diseases due to alcohol consumption. (C) 2015 Elsevier B.V. All rights reserved.