Intracellular glucose concentration in small and large rat adipose cells

Intracellular free glucose concentrations have been estimated in small and large isolated epididymal adipose cells prepared from young lean and older obese rats using glucose-induced steady-state tracer 3-O-methylglucose countertransport. Steady-state 3-O-methylglucose uptake was measured in the presence of 2--50 mM glucose or sucrose in the absence or presence of 100 microU insulin/ml. The ratio of the uptake of 3-O-methylglucose in the presence of glucose to that in the presence of sucrose at each sugar concentration was then utilized to estimate the corresponding intracellular glucose concentration. At all three extracellular glucose concentrations tested in the absence of insulin, intracellular concentrations of glucose are greater in the large cells than in the small cells. In the presence of 2 mM glucose and insulin, on the other hand, intracellular glucose concentrations of 2 mM are attained, regardless of cell size. These results suggest that transport may not be the rate-limiting step for glucose metabolism at physiologic glucose concentrations either in the enlarged adipose cell in the absence or presence of insulin or in the small adipose cell in the presence of maximally stimulating concentrations of insulin.