Uptake of gold-labeled Stx2. HUVECs treated with gold-labeled Stx2 were fixed after 1 hour (A) and 4 hours (B) and scanned with a transmission electron microscope. Black beads, marked intracellularly with white arrowheads, correspond to gold-labeled Stx2. Uptake of Stx2 and intracellular distribution after one hour is visualized in panel A. At 4 hours most of the toxin is detected intracellularly as shown in panel B. ER indicates endoplasmic reticulum; N, nucleus.