Bulk solute extrusion as a mechanism conferring solute uptake specificity by pinocytosis in Amoeba proteus

A variety of positively charged solutes induce pinocytosis in Amoeba proteus, ranging from metabolically useful material to solutes that may prove harmful, such as Alcian blue. Alcian blue is taken up by pinocytosis and then a fraction of the accumulated dye is expelled in bulk form through "extrusion channels." This response is not elicited by other solutes taken up by pinocytosis in the amoeba, implying that if any selectivity is associated with this process, it is by specific solute extrusion mechanisms in the cytoplasm.