title: Inhibition of pinocytosis in rat embryo fibroblasts treated with monensin.
abstract: Rat embryo fibroblasts cultured in the presence of monensin exhibited an inhibited uptake of horseradish peroxidase. The inhibition was detected after 3 h, after which time the cells became increasingly vacuolated; the concentration of monensin required to inhibit pinocytosis (0.4 microM for half-maximum inhibition at 18 h) was similar to that found by others to inhibit secretion. Both the exchange of 5'-nucleotidase between the membranes of cytoplasmic organelles and the cell surface and the internalization of anti-5'-nucleotidase bound to the cell surface were inhibited by approximately 90% in monensin-treated cells. The effects of monensin were reversible: cells cultured first with monensin, and then in fresh medium, exhibited control levels of horseradish peroxidase uptake, exchange of 5'-nucleotidase, and internalization of anti-5'-nucleotidase bound to the cell surface. After monensin treatment, the median density of both galactosyl transferase and 5'-nucleotidase increased from 1.128 to 1.148, and the median density of both N-acetyl-beta-glucosaminidase and horseradish peroxidase taken up by endocytosis decreased from 1.194 to 1.160. The results indicate that monensin is a reversible inhibitor of pinocytosis and, presumably, therefore, of membrane recycling. They suggest that the inhibition of membrane recycling occurs at a step other than the fusion of pinocytic vesicles with lysosomes and is perhaps a consequence of an effect of the ionophore on the Golgi complex.
mesh_terms: D015720:5'-Nucleotidase; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D005347:Fibroblasts; D005663:Furans / Q000494:pharmacology*; D006735:Horseradish Peroxidase; D007425:Intracellular Membranes / Q000201:enzymology; D008247:Lysosomes / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology*; D009708:Nucleotidases / Q000378:metabolism; D010873:Pinocytosis / Q000187:drug effects*; D014176:Protein Biosynthesis; D051381:Rats; D014617:Vacuoles / Q000648:ultrastructure
chemical_list: D005663:Furans; D000255:Adenosine Triphosphate; D008985:Monensin; D006735:Horseradish Peroxidase; D009708:Nucleotidases; D015720:5'-Nucleotidase