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Monensin inhibits ligand dissociation only transiently and partially and distinguishes two galactosyl receptor pathways in isolated rat hepatocytes
Author(s) -
Oka Janet A.,
Weigel Paul H.
Publication year - 1987
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041330207
Subject(s) - monensin , receptor , dissociation (chemistry) , chemistry , biophysics , intracellular , ligand (biochemistry) , biochemistry , stereochemistry , microbiology and biotechnology , biology
Monensin has been shown to inhibit the dissociation of internalized asialoorosomucoid (ASOR) from galactosyl (Gal) receptors in hepatocytes (Harford et al., J. Cell. Biol., 96 : 1824, 1983). Examination of the long‐term kinetics of dissociation of a single round of surface‐bound 125 I‐ASOR in the presence of monensin revealed, however, that dissociation resumed after a lag of 30–40 min. Dissociation proceeded slowly with apparent first order kinetics (k = 0.006–0.022 min −1 ) and reached a plateau after 4 h, both in freshly isolated cells in suspension and in cells cultured for 24 h. Only a portion of the ligand bound to surface Gal receptors was capable of dissociating. The degree of dissociation was correlated with the expression of a subpopulation of receptors we have recently designated as state 1 Gal receptors (Weigel et al., Biochem. Biophys. Res. Commun. 140 : 43, 1986). The recovery and dissociation of a portion of 125 I‐ASOR‐receptor complexes after the lag period is not due to a depletion of monensin, since a second addition of the drug has no affect once dissociation resumes. Furthermore, as assessed by the accumulation of the fluorescent dye acridine orange, cells have not recovered the ability to acidify intracellular compartments during the time that dissociation occurs. The results support a model for the hepatic Gal receptor system, in which there are two functionally different receptor populations, recycling pathways, and ligand processing pathways. Monensin blocks dissociation of 125 I‐ASOR from receptors in the major pathway completely. In the minor pathway dissociation proceeds to completion only after a lag. In this minor pathway monensin appears to temporarily delay a maturation or translocation process that must occur prior to dissociation. We conclude that the observed dissociation in the presence of monensin cannot be mediated by low pH, or by pH or pNa gradients.