Mechanism of stimulation of pinocytosis by trypan blue

Trypan blue at 50 microgram/ml stimulates the pinocytic uptake of 125I-labelled PVP, but not of colloidal 198Au or formaldehyde-denatured 125I-labelled bovine serum albumin, by the 17.5-day rat visceral yolk sac incubated in vitro. Neither Trypan blue nor a combination of the dye with 125I-labelled PVP stimulated the rate of pinocytosis of liquid by the tissue. Trypan blue itself was shown to enter the yolk-sac cells by adsorptive pinocytosis. It is proposed that an interaction between Trypan blue and 125I-labelled PVP enables the latter substrate to enter the cells adsorptively by so-called 'piggy-back' pinocytosis.