Endocytosis: the different energy requirements for the uptake of particles by small and large vesicles into peritoneal macrophages

The uptake of various, different-sized particles by macrophages was studied using the electron microscope. In addition to observing normal cells, cells were examined which had been inhibited by exposing them to low temperature (4 degrees C), and to a number of metabolic poisons. It was found that large particles (>0.1 mu m) enter the cells and are contained in large vesicles (0.14 mu m). Small particles (<50 nm) may also enter the cells by this process. They enter most frequently, however, by passing into small (similar to 70 nm) vesicles. These may later coalesce and their contents adhere to give a second kind of large vesicle. The various inhibitors prevented the ingestion of the large particles (and of the small particles en masse) into large vesicles, but did not prevent their initial adsorption onto the plasma membranes. They did not prevent nearly normal numbers of small particles from entering the pre-existing small vesicles, nor their subsequent fusion into the second class of large vesicles.