Serum-dependence of fluid-phase pinocytosis and specificity in adsorptive pinocytosis of simple proteins in rat peritoneal macrophages.

An increase in the concentration of serum resulted in a very marked increase in the rate of fluid-phase pinocytosis in rat peritoneal macrophages, as measured by the uptake of 125I-labelled polyvinylpyrrolidone. In contrast, the rate of uptake of colloidal [198Au]gold, an adsorptive substrate, decreased when the serum concentration was increased. This lessened uptake of colloidal gold must be due to competition by serum components. Studies on the specificity of pinocytosis of simple proteins, using 125I-labelled H4 and M4 forms of porcine lactate dehydrogenase, and formaldehyde-denatured and untreated bovine serum albumin as substrates, suggest that positive charge and hydrophobicity determine adsorptive pinocytosis of simple proteins in peritoneal macrophages. The rate of fluid-phase pinocytosis and the specificity of adsorptive pinocytosis in peritoneal macrophages are very similar to those reported for Kupffer cells.