Effect of extracellular matrix on HKa-induced endonucleolytic DNA cleavage. Endothelial cells cultured on different extracellular matrix proteins were stimulated with 10 ng/mL bFGF in the absence or presence of 50 nM HKa for 12 hours. Cytoplasmic DNA was then isolated as described under “Detection of endothelial-cell apoptosis” in “Materials and methods” and analyzed using 1% agarose gel electrophoresis. Agarose gels were stained with ethidium bromide to detect fragmented DNA. Vn indicates vitronectin; Fn, fibronectin; Ln, laminin; col I, type I collagen; and col IV, type IV collagen.