Active Rac1 reduces neovessel leakiness associated with VEGF-driven pathologic angiogenesis. (A) VEGF₁₆₅ transfectants were mixed with packaging cells expressing retrovirus encoding active L61Rac1 or empty vector (control) and injected together with Matrigel subdermally. Seven days later neovessel leakiness was assessed by confocal microscopy. Intravascular tracer was visualized with Texas Red-dextran (molecular weight, 70 kDa) injected 1 minute before killing (left). FITC-dextran (molecular weight, 70 kDa) injected 20 minutes before killing was used to visualize the sum of (intravascular tracer + extravascular tracer) (center). The extent of tracer extravasation was determined by subtracting the Texas Red signal from the respective FITC-dextran signal to yield the signal for extravascular tracer corresponding to tracer leakage (right). (B) Quantification of tracer leakage was achieved by integrating the signal intensities for the resultant extravasated tracer (n = 4 for both groups). Active Rac1 reduced tracer leakage > 4-fold. Scale bar = 200 μm.