Insulin Binding and Insulin Action in Cultured Fibroblasts: Significant Differences between a Phosphoglucose Isomerase-Deficient Mutant and the Parental Strain

The interrelationships of hexose feeding and insulin action were studied in the Chinese hamster fibroblast cell lines 023 and DS-7. The latter, derived from 023 and deficient in phosphoglucose isomerase, has been used to map the metabolic requirements for aldohexose-mediated down-regulation or ``curbing'' of hexose transport. We have characterized insulin binding and the response to insulin in both cell lines to determine if the insulin-mediated stimulation of transport is similarly dependent on hexose metabolism. DS-7 cells exhibited 5-6 times as many high-affinity insulin binding sites as the parental strain. Apart from this difference, 023 and DS-7 cells showed comparable insulin binding characteristics, which are similar to those observed in other cell types. Insulin at a concentration of 1 μ g/ml (167 nM) was found to stimulate 3-O-methylglucose uptake by ≈ 50% in glucose-fed cells of both lines. In neither line did glucose starving significantly alter insulin binding or the insulin-induced stimulation of transport. Feeding with mannose or fructose was found to increase both parameters in 023 cells but had no effect on DS-7 cells. The increase in hexose uptake with the administration of insulin or with glucose starving was shown to be due to an increase in Vmax. Our studies suggest that (i) insulin binding and effect are not regulated by hexose metabolism in the same manner as in the curbing process and (ii) insulin induces the recruitment of a transporter pool that is insensitive to hexose curbing.