title: Uptake and destruction of 125I-CSF-1 by peritoneal exudate macrophages.
abstract: The binding and uptake of the colony-stimulating factor CSF-1 by peritoneal exudate macrophages (PEM) from lipopolysaccharide insensitive C3H/HeJ mice was examined at 2 degrees C, and at 37 degrees C. At 2 degrees C, 125I-CSF-1 was bound irreversibly to the cell surface. At 37 degrees C, 90% of the cell surface associated 125I-CSF-1 was rapidly internalized and subsequently degraded and the remaining 10% dissociated as intact 125I-CSF-1. Thus classical equilibrium or steady state methods could not be used to quantitatively analyze ligand-cell interactions at either temperature, and alternative approaches were developed. At 2 degrees C, the equilibrium constant (Kd less than or equal to 10(-13) M) was derived from estimates of the rate constants for the binding (kon congruent to 8 x 10(5) M-1 s-1) and dissociation (koff less than or equal to 2 x 10(-7) s-1) reactions. At 37 degrees C, the processes of dissociation and internalization of bound ligand were kinetically competitive, and the data was formally treated as a system of competing first order reactions, yielding first order rate constants for dissociation, koff = 0.7 min-1 (t1/2 = 10 min) and internalization, kin = 0.07 min-1 (t 1/2 = 1 min). Approximately 15 min after internalization, low-molecular weight 125I-labeled degradation products began to appear in the medium. Release of this degraded 125I-CSF-1 was kinetically first order over three half-lives (Kd = 4.3 x 10(-2) min-1, t1/2 = 16 min). Thus CSF-1 binds to a single class of receptors on PEM, is internalized with a single rate limiting step, and is rapidly destroyed without segregation into more slowly degrading intracellular compartments.
authors.affiliation: Department of Microbiology & Immunology, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: L J
authors.initials: LJ
authors.lastname: Guilbert
authors.forename: P W
authors.initials: PW
authors.lastname: Tynan
authors.forename: E R
authors.initials: ER
authors.lastname: Stanley
mesh_terms: D000818:Animals; D001345:Autoradiography; D001386:Azides / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002738:Chloroquine / Q000494:pharmacology; D003847:Deoxyglucose / Q000494:pharmacology; D004705:Endocytosis; D007700:Kinetics; D008247:Lysosomes / Q000187:drug effects; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008744:Methylamines / Q000494:pharmacology; D051379:Mice; D008809:Mice, Inbred C3H; D010529:Peritoneal Cavity / Q000166:cytology; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D013696:Temperature
chemical_list: D001386:Azides; D008744:Methylamines; D016173:Macrophage Colony-Stimulating Factor; D002738:Chloroquine; D003847:Deoxyglucose; C027451:methylamine; D016186:Receptor, Macrophage Colony-Stimulating Factor