Insulin stimulation of glucose entry in cultured human fibroblasts

Abstract

The effect of insulin on glucose entry has been studied in monolayer cultures of human diploid fibroblastic cells. Influence of insulin on total cell glucose incorporation was evaluated using [¹⁴C] glucose. Glucose incorporation was increased up to two‐fold in the presence of insulin. Insulin action occurred within 30 minutes and could be observed with insulin concentrations as low as 10⁻¹⁰ M (10 μU/ml). The action of insulin was enhanced by preincubation in glucose‐free medium. After glucose starvation the cells converted glucose primarily to glycogen and nucleotides, and the stimulation by insulin was observed equally in both fractions. Influence of insulin on the kinetics of hexose transport was studied using 2‐deoxyglucose and 3‐0‐methyl glucose. A large diffusion component was corrected using ρ‐chloromercuribenzoic acid or phloridzin. K_m for facilitated diffusion averaged 1.9 mM for 2‐deoxyglucose and 5.3 mM for 3‐0‐methyl glucose, and V_max ranged from 10–24 nmoles/min/mg cell protein. Insulin resulted in a 150% increase in V_max with no significant change in K_m. The data suggest that human diploid fibroblasts can be a useful system for the study of insulin's glucoregulatory action.