title: Possible dissociation between insulin binding and insulin action in isolated fetal rat hepatocytes.
abstract: To directly examine the relationship between insulin receptors and insulin action in fetal tissue, we compared insulin receptor characteristics and insulin-mediated 14C-glucose incorporation into glycogen, as well as glycogen synthase activity, in freshly isolated hepatocytes from 21-day fetal (F) and adult (A) rats. Viability of hepatocytes was documented by trypan blue exclusion (greater than 90%), time-dependent 14C-leucine incorporation into protein, and dose-related incorporation of glucose into glycogen. Percent specific binding of 125I-insulin per unit protein was significantly higher in F than A liver plasma membranes (32.2 +/- 0.3 versus 18 +/- 2.4; P less than 0.01) and Scatchard plots revealed twice the number of receptors in F. Similarly, receptor number per cell surface area was threefold higher in F than in A (150 versus 50 sites/micron2). At a fixed medium glucose concentration of 11.2 mM, insulin stimulated 14C-glucose incorporation into glycogen in a dose-related manner in A with an apparent Km of 1.0 ng/ml and Vmax at 5-10 ng/ml corresponding to 30-40% of total receptor occupancy; no effect was obtained in F with insulin up to 100 ng/ml. Net glucose incorporation into glycogen (nmol/10(6) cells/h) increased progressively with increasing medium glucose concentrations ranging from 1.4 to 27.8 mM; incorporation by F was significantly greater than by A at each glucose concentration. However, whereas insulin at 100 ng/ml significantly augmented net glucose incorporation at each glucose concentration in A, no effect of insulin was apparent in F.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000375:Aging; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D005333:Fetus / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D008112:Liver Glycogen / Q000096:biosynthesis; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism
chemical_list: D007328:Insulin; D008112:Liver Glycogen; D006006:Glycogen Synthase; D011972:Receptor, Insulin; D005947:Glucose