Using a rat myofibroblast-like hepatic stellate cell line, We Studied the actomyosin-based cytoskeletal actions mediated by Rho-kinase and/or myosin light chain kinase (MLCK). Calmodulill/MLCK inhibitors W-7 and ML-7 attenuated cell migration dose-relatedly at concentrations from 10(-6) to 10(-4) M and collagen gel-contraction by the cells at 10(-4) M, respectively. Rho-kinase inhibitors Y-27632 and HA1077 attenuated the gel-contraction at concentrations from 10(-6) to 10(-4) M, respectively. These Rhokinase inhibitors attenuated cell migration at 10(-7) M but enhanced the migration at 10(-4) M, respectively. They altered cell morphology showing prominent peripheral actin bundles and sparse central stress fibers, in comparison with the Calillodulin/MLCK inhibitors. Both ML-7 and Y-27632 attenuated phosphorylation of myosin regulatory light chain and cell attachment to extracellular substrate. ML-7 attenuated the activation of GTP-binding protein Rac, while Y-27632 did not. These findings suggest that the actomyosin-based cytoskeletal actions can be functionally diverse depending on the Rho-kinase-mediated pathway and the MLCK-mediated pathway. (C) 2003 Elsevier Science (USA). All rights reserved.