Control of glucose transport in adipose tissue of the rat: Role of insulin, ATP, and intracellular metabolites

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Abstract
The purpose of this study was to elucidate some of the mechanisms of control of the glucose transport step in adipose tissue. Glucose trnasport was studied by monitoring the conversion of [1-14C]glucose to 14CO2 in a system where glucose transport was made rate limiting by increasing the flux through the pentose phosphate pathway with phenazine methosulfate [PM], an agent which results in rapid rates of reoxidation of NADPH. The maximum velocity for the apparent rate of glucose transport was increased significantly by insulin. There was no change in the glucose concentration required for half-maximal rates of 14CO2 production. Glucose transport was also monitored by directly measuring the rate of glucose uptake. Glucose uptake was increased by PM. The intracellular G-6-P concentration was decreased by PM. These 2 agents, insulin and PM, seemed to act by independent mechanisms as their optimal effects on glucose uptake were additive. The apparent rate of glucose transport was decreased by ATP which resulted in a decrease in maximal velocity, but did not affect the affinity for glucose. This effect of ATP was seen in the presence or absence of insulin.