Pinocytosis and phagocytosis: the effect of size of a particulate substrate on its mode of capture by XXXX peritoneal macrophages cultured in vitro.

@entity852 @entity4280 @entity2389 @entity3812 @entity35
Both phagocytosis (of particles) and pinocytosis (of solutes) occur in macrophages. It is not known, however, whether particles, if they are small enough, can enter by pinocytosis, nor whether there is a minimum size of particle capable of triggering phagocytic uptake. These questions have been investigated by studying, in vitro, the uptake by @entity35 peritoneal macrophages of particles ranging in diameter from 30 nm to 1100 nm. Percoll (30 nm diameter) and @entity852 beads (100, 300, 600, 800 or 1100 nm diameter) were 125I-iodinated and their uptake by macrophages was measured in the absence or presence of metabolic and cytoskeletal inhibitors. Since uptake, expressed as an Endocytic Index (microliter/10(6) cells per h), increased steadily with the duration of incubation and was inhibited by low temperature or metabolic inhibitors, it was concluded that true endocytosis, and not a superficial cell-association, was being measured. Rates of clearance increased with increasing particle diameter. The rate of uptake of Percoll was 10-times, and of 100 nm @entity852 beads 100-times, the rate of fluid-phase pinocytosis, as measured by the uptake of 125I-labelled @entity4280 . @entity852 beads of 1100 nm diameter were captured at 700-times this rate. The differential effects of @entity3812 and @entity2389 on the uptake of 125I-labelled @entity4280 and of 1100 nm @entity852 beads were taken as indicators of their effects on pinocytosis and phagocytosis respectively. It is concluded that Percoll, although particulate, is captured by pinocytosis. The pattern of inhibition of uptake of @entity852 particles suggests that there is no radical discontinuity between pinocytic and phagocytic uptake, but that the contribution of phagocytosis steadily increases with increasing particle diameter. The results are discussed.
