Insulin stimulation of glycogen synthase activity in cultured human fibroblasts from diabetic and control subjects

Abstract

The influence of insulin on the enzyme glycogen synthase was studied in cultured skin fibroblasts from 5 non-diabetic subjects and 3 diabetic patients. Confluent fibroblast cultures were maintained in serum-free medium for 24 hours before exposure to graduated concentrations of insulin (0.1 to 2000 mU/ml) for one hour. The independent form of glycogen synthase activity (determined in the absence of glucose-6-phosphate) was increased in some experiments by exposure of cells to 0.1mU of insulin/ml; 1.0mU/ml produced a consistent increase; but at least 1000 mU/ml was required for maximum effect. In the non-diabetic subjects, the mean baseline total activity of glycogen synthase was 0.182 ~mol/mg protein/h with 16.8% in the independent form; with 1000 m U of insulin/ml the total activity was 0.167 gmol/mg/h with 45.4% in the independent form. In the diabetic fibroblasts, the mean percentage of glycogen synthase in the independent form was lower than in the control cells at baseline and with all concentrations of insulin utilised; at baseline, total activity was 0.117 ,umol/mg protein/h with 11.7% in the independent form while with 1000mU of insulin/ml the values were 0.146 ~tmol/mg protein/h and 30.7% respectively. Demonstration of an effect of insulin on glycogen synthase in human fibroblasts provides another phenomenon for comparison in cells from control subjects and diabetic patients.

Characteristics of Normal and Maturity-Onset Diabetic, (Type II Diabetes) Cell Cultures:, Life Spans and DNA Synthetic Capabilities

“…This in fact agrees with recent reports from other groups showing no insulin response differences in normal vs. type I. i.e. on glycogen synthesis [Craig et al, 1980], or vs. type II; on protein and RNA synthesis [Eckel and Fujimoto, 1981], insulin binding [Prince et al, 1981], glucose uptake [Howard et al" 1980], CO; production [Goldstein and Littlefield, 1969] and amino acid transport [Gelehner et al, 1981], In summary, we have presented a large body of data covering several parameters basic to the in vitro aging and growth of the cell with the purpose of uncovering inherent differences between normal and type II dia betic cells. No age-or growth-related differ ences have been uncovered and we feel that at this point the inherent cell defect does not revolve around the parameters studied here in.…”

In Vitro Studies of Insulin Resistance in Patients With Lipoatrophic Diabetes: Evidence for Heterogeneous Postbinding Defects

“…Under our experimental conditions, glucose entry was no longer rate limiting, due to the marked increase in passive diffusion that accounts (at 5.5 mM glucose) for the greatest part of glucose entry (data not shown), as previously reported (5,6). This test seems to be easier to interpret than the assay of giycogen synthase activity, which is often used (7,29); both total activity and the percentage of the active form need to be evaluated. These values are related to the giycogen cell content and could vary in opposite directions (30).…”

Regulation of Glycosaminoglycan Synthesis by Thyroid Hormone in Vitro

“…They are known to retain hormone receptors for triiodothyronine, dexamethasone, insulin, and androgen (5)(6)(7)(8). Responses to several hormones including glucocorticoids, prostaglandins, cathecholamines, and insulin have been demonstrated in fibroblasts (9)(10)(11)(12)(13). 'Abbreviations used in this paper: BS, bovine serum; D-FCS, thyroid hormone-depleted FCS; D-FCS + T3, D-FCS to which T3 was added; FCS, fetal calf serum; GAG, glycosaminoglycans; HA, hyaluronic acid; T3, triiodothyronine, T4, tetraiodothyronine or thyroxine; Tx-BS, BS from thyroidectomized animals; Tx-BS + T3, Tx-BS with added T3; UDPGlcNAc, uridine disphosphate-N-acetyl glucosamine; UDPGJcUA, uridine diphosphate glucuronic acid.…”