Rho/Rok Inhibitor. HA-1077 is a small, cell permeable derivative of isoquinoline which specifically inhibits the small GTPase - Rho by inhibition of its associated kinase-Rho dependent kinase (ROK). This signaling pathway acts as a molecular switch to control cytoskeleton organization in many cell types including smooth muscle. By inhibition of ROK, HA-1077 decreases the myosin light chain (MLC) phosphorylation induced by Ca2+ due to abrogating Rho-mediated inhibition of MLC dephosphorylation. HA-1077 also inhibits fetal calf serum-induced proliferation and \[\\3\\H]\thymidine incorporation into DNA of growth-arrested VSMC in a dose-dependent manner. At concentrations higher than 5 μM, it induces disorganization of actin filament structure. This compound was also found to act as a vasodilator and antivasospasm drug which antagonizes the verapamil-insensitive voltage dependent Ca2+ channel and is used clinically for treatment of the cerebral vasospasm after subarachnoid hemorrhage. Cell Signaling Activators and Inhibitors; Rho/Rok Inhibitor.