Figure 1.

Immunoreactive type IV collagen and intact tube formation by endothelial cells require the presence of a physiological concentration of ascorbic acid. Type IV collagen production by HUVECs in 0 to 200 µM ascorbic acid was measured by ELISA. (A) Representative photomicrographs of tube formation on Matrigel basement membrane matrix in 0 to 200 µM ascorbic acid (original magnification, x40). (B) Intact tubes formed on Matrigel in 0 to 200 µM ascorbic acid were enumerated (original magnification, x40) (C).