Receptor-mediated insulin degradation and insulin-stimulated glycogenesis in cultured foetal hepatocytes.
Insulin-stimulated glycogenesis and insulin degradation were studied simultaneously at 37 degrees C in cultured foetal hepatocytes grown for 2-3 days in the presence of cortisol. Degradation of cell-associated insulin, as measured by trichloroacetic acid precipitation, was significant after 4 min in the presence of 1-3 nM-125I-labelled insulin. This process became maximal (30% of insulin degraded) after 20 min, a time when binding-state conditions were achieved. No insulin-degradative activity was detected in a medium that had been exposed to cells. At steady-state, the appearance of insulin degradation products in the medium was linearly dependent on time (1.5 fmol/min per 10(6) cells at 1nM-125I-labelled insulin). Chloroquine (3-50 microM), bacitracin (0.1-10 mM) and NH4Cl (1-10 mM) inhibited insulin degradation as soon as this became detectable and caused an increase in the association of insulin to hepatocytes after 20 min. Lidocaine and dansylcadaverine had similar effects, whereas N-ethylmaleimide, aprotinin, phenylmethanesulphonyl fluoride and leupeptin were found to be ineffective. Chloroquine, and also bacitracin, at concentrations that inhibited insulin degradation, decreased the insulin-stimulated incorporation of [14C]glucose into glycogen over 2 h. This effect of chloroquine was specific, since it did not modify the basal glycogenesis, or the glycogenic effect of a glucose load in the absence of insulin. It therefore appears that the receptor-mediated insulin degradation (or some associated pathway) is functionally related to the glycogenic effect of insulin in foetal hepatocytes.
D000818:Animals; D001414:Bacitracin / Q000494:pharmacology; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D008112:Liver Glycogen / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism*
D007328:Insulin; D008112:Liver Glycogen; D001414:Bacitracin; D002738:Chloroquine; D011972:Receptor, Insulin; D005947:Glucose