title: Loss of surface galactosyl receptor activity on isolated rat hepatocytes induced by monensin or chloroquine requires receptor internalization via a clathrin coated pit pathway.
abstract: We studied the effect of hyperosmotic inhibition of the clathrin coated pit cycle on the monensin- and chloroquine-dependent loss of surface galactosyl (Gal) receptor activity on isolated rat hepatocytes. Cells treated for 60 min without ligand at 37 degrees C with 25 microM monensin or 300 microM chloroquine in normal medium (osmolality congruent to 275 mmol/kg) bound 40-60% less 125I-asialo-orosomucoid (ASOR) at 4 degrees C than untreated cells. Cells exposed to monensin or chloroquine retained progressively more surface Gal receptor activity, however, when the osmolality of the medium was increased above 400 mmol/kg (using sucrose as osmolite) 10 min prior to and during drug treatment. Cells pretreated for 10 min with hyperosmolal media (600 mmol/kg) alone internalized less than or equal to 10% of surface-bound 125I-ASOR. Thus, the ligand-independent loss of surface Gal receptor activity on monensin- and chloroquine-treated hepatocytes requires internalization of constitutively recycling receptors via a coated pit pathway.
authors.affiliation: Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston 77550.
authors.forename: D D
authors.initials: DD
authors.lastname: McAbee
authors.forename: J A
authors.initials: JA
authors.lastname: Oka
authors.forename: P H
authors.initials: PH
authors.lastname: Weigel
mesh_terms: D000818:Animals; D002738:Chloroquine / Q000494:pharmacology*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism / Q000502:physiology*; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000502:physiology*; D005690:Galactose / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D008297:Male; D008985:Monensin / Q000494:pharmacology*; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology
chemical_list: D011956:Receptors, Cell Surface; C039707:galactose receptor; D002738:Chloroquine; D008985:Monensin; D005690:Galactose