Effects of Insulin and Insulin-like Agents on the Glucose Transport System of Cultured Human Fibroblasts

Abstract

We have studied the effects of insulin and insulin-like agents on glucose transport by cultured human fibro-blast monolayers. Initial rates of glucose transport were determined by measurement of 2-deoxy-D-glu-cose uptake. At physiologic concentrations, insulin stimulates 2-deoxy-D-glucose transport (average of 50% over basal) with a half-maximally effective insulin concentration of 3.3 ± 0.9 ng/ml. This effect of insulin is rapid and is half-maximal at 10 min and becomes maximal by about 30 min. Kinetic analyses showed that insulin increased the transport Vmax from 7.4 ± 0.9 nmol/min/106 cells to 11.0 ± 1.5 nmol/min/106 cells and had no effect on the Km value (2.5 ± 0.3 mM). While glucose starvation led to a higher overall rate of 2-deoxy-D-glucose transport, the relative stimulation by insulin was the same as in non-glucose-starved cells. Insulin mimickers [insulin-like growth factor (IGF), anti-insulin receptor antibody, and concanavalin A] also stimulate 2-deoxy-D-glucose transport by human fibroblast monolayers in a dose-dependent manner and the maximal effects of IGF and anti-insulin receptor antibody were the same as that of insulin, while the maximal effect of concanavalin A was only 78% of that of insulin. The maximal effects of either insulin and IGF or insulin and anti-insulin receptor antibody were not additive, suggesting that these agents all act via the same glucose transport effector system in human fibroblasts. In conclusion, human fibroblasts possess an insulin-sensitive glucose transport system that displays many of the characteristics common to other more well studied transport systems. Thus, cultured human fibroblasts can serve as an important model for physiologic studies of insulin action and glucose transport, and for studies of pathophysiologic abnormalities of these processes in cells obtained from patients with various disease states.