Fig. 1. Plasma kallikrein induced MMP-1 activation and contraction of endothelial tube networks. ECs were suspended in collagen matrices and plated in 96-well tissue culture plates (4.5 mm diameter) (A) or 384 micro-well plates (3 mm square) (B). Culture media contained plasma kallikrein at 1 µg/ml. The same culture well was photographed at the indicated times (in hours) during the capillary tube regression and collagen gel contraction process. (C) Conditioned media were collected and triplicate cultures were examined for evidence of capillary tube regression and collagen gel contraction (+ indicates occurrence of gel contraction). Samples were run on SDS-PAGE gels, blotted to PVDF membranes and probed with anti-MMP-1 antibodies. Arrows indicate the position of MMP-1 zymogen and arrowheads indicate activated MMP-1. Note the absence of activated MMP-1 (arrowhead) in the absence of kallikrein. Bar, 500 µm.