Role of myosin IIA and Rho kinase in regulating the stability of the primary hemostatic plug. Vascular injury was induced in the mesenteric postcapillary venules of anesthetized C57/Bl6 mice by needle puncture, in the presence of lepirudin (50 mg/kg, administered intravenously prior to injury). In the indicated experiments, the effects of blebbistatin, an inactive enantiomer of blebbistatin (control), vehicle (DMSO), or H1152 on thrombus stability was assessed following repetitive injections (denoted by ▀), with concentrations and volumes as described in “Intravital microscopy.” (A) The relative change in surface area of a given thrombus over time was determined off-line, and expressed relative to the initial surface area of the thrombus prior to injection. These results depict data taken from 1 of 4 independent experiments, with representative images from one such experiment depicted in panel B. (C) The percentage decrease in thrombus size following each infusion of vehicle/inhibitor was quantified as described in “Intravital microscopy,” and expressed as a percentage (%) of the original thrombus prior to infusion. These results represent the mean plus or minus SEM (n = 4), where *** indicates P < .001.