title: Glucose and insulin co-regulate the glucose transport system in primary cultured adipocytes. A new mechanism of insulin resistance.
abstract: We have previously shown in primary cultured rat adipocytes that insulin acts at receptor and multiple postreceptor sites to decrease insulin's subsequent ability to stimulate glucose transport. To examine whether D-glucose can regulate glucose transport activity and whether it has a role in insulin-induced insulin resistance, we cultured cells for 24 h in the absence and presence of various glucose and insulin concentrations. After washing cells and allowing the glucose transport system to deactivate, we measured basal and maximally insulin-stimulated 2-deoxyglucose uptake rates (37 degrees C) and cell surface insulin binding (16 degrees C). Alone, incubation with D-glucose had no effect on basal or maximal glucose transport activity, and incubation with insulin, in the absence of glucose, decreased maximal (but not basal) glucose transport rates only 18% at the highest preincubation concentration (50 ng/ml). However, in combination, D-glucose (1-20 mM) markedly enhanced the long-term ability of insulin (1-50 ng/ml) to decrease glucose transport rates in a dose-responsive manner. For example, at 50 ng/ml preincubation insulin concentration, the maximal glucose transport rate fell from 18 to 63%, and the basal uptake rate fell by 89%, as the preincubation D-glucose level was increased from 0 to 20 mM. Moreover, D-glucose more effectively promoted decreases in basal glucose uptake (Ki = 2.2 +/- 0.4 mM) compared with maximal transport rates (Ki = 4.1 +/- 0.4 mM) at all preincubation insulin concentrations (1-50 ng/ml). Similar results were obtained when initial rates of 3-O-methylglucose uptake were used to measure glucose transport. D-glucose, in contrast, did not influence insulin-induced receptor loss. In other studies, D-mannose and D-glucosamine could substitute for D-glucose to promote the insulin-induced changes in glucose transport, but other substrates such as L-glucose, L-arabinase, D-fructose, pyruvate, and maltose were without effect. Also, non-metabolized substrates which competitively inhibit D-glucose uptake (3-O-methylglucose, cytochalasin B) blocked the D-glucose plus insulin effect.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D019325:3-O-Methylglucose; D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000378:metabolism; D004357:Drug Synergism; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007333:Insulin Resistance; D007700:Kinetics; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007328:Insulin; D008757:Methylglucosides; D019325:3-O-Methylglucose; D003847:Deoxyglucose; D005947:Glucose