Effect of pH and 3-Hydroxybutyrate on Insulin Binding and Action in Cultured Human Fibroblasts

The influence of pH and 3-hydroxybutyrate on insulin binding and action has been studied in cultured human fibroblasts. When the pH of the incubation medium was decreased from 7.6 to 6.8, insulin stimulation of glycogen synthase and total glucose uptake was decreased. The decreased pH induced both an increase in the insulin concentration for half-maximal response, and a decrease in maximal responsiveness. When insulin binding was measured at lower pH, receptor affinity was decreased. The effect of 3-hydroxybutyrate on insulin binding and action was assessed at pH 7.4 and 6.9. In the presence of 3-hydroxybutyrate, insulin binding increased, but insulin action on glycogen synthase and total glucose uptake was unaffected. The data show that insulin action is impaired at lower pH. The decreased sensitivity is probably related to the decrease in insulin binding affinity at lower pH, but decreased maximal responsiveness implies that postreceptor components are also affected by lower pH. The results also suggest that 3-hydroxybutyrate induced a dissociation between binding and response, since an increase of insulin binding was not accompanied by changes in the regulation of glycogen synthase and total glucose uptake.