Fig. 6. Vero cells that do not bind Shiga or Cholera toxin also lack internal toxin receptors. (a) CTX-binding cells. The left panels (two different experiments) show cells strongly binding Cy3-CTX to the cell surface. The same cells also exhibit a strong binding of Cy5-CTX to internal binding sites after permeabilization, whereas cells that bind little Cy3-CTX to the surface lack internal binding sites for Cy5-CTX. (b) (Upper panels) A cell that strongly binds to Cy2-ST also expresses internal binding sites for Cy5-ST. (Lower panels) Two cells that exhibit strong binding of Cy2-ST to the cell surface also show internal receptors for Cy5-ST after cell permeabilization. Note that surrounding cells that possess almost no internal binding sites fail also to bind ST to the cell surface.