Northern blot analysis of endothelial GPIbα mRNA. Poly(A+) mRNA were extracted and analyzed by Northern blot using radiolabeled GPIbα cDNA (A) or vWF cDNA (B) as the probe in the different cell extracts: primary endothelial cells (4 × 10⁶ cells, lanes 1 and 2), second passage endothelial cells (7 × 10⁶ cells, lanes 3 and 4), and HEL 5J20 cells (7 × 10⁶ cells, lane 5). mRNA expression was observed in unstimulated (lanes 1 and 3) endothelial cells or after TNFα treatment (lanes 2 and 4). The position of GPIbα mRNA is indicated by an open arrow corresponding to 2.8 kb, whereas vWF mRNA band is shown by a solid arrow (9 kb).