Studies on the Action of Insulin in Isolated Adipose Tissue Cells

Abstract 1. Insulin stimulated the incorporation of 32P-labeled inorganic phosphate into acid-soluble mononucleotides in isolated fat cells incubated in the absence of glucose in the medium. The specific radioactivity of the ATP increased by approximately 60%. 2. This increase was accompanied by a small but significant increment in steady state concentration of ATP over control. 3. Experiments with previously labeled cells, incubated in the absence of phosphate in the incubation medium, suggest that this stimulation by insulin of mononucleotide labeling was not a result of an effect of insulin on active transport across the plasma membrane. 4. Lipolytic agents, which are known to increase the concentration of cyclic AMP in adipose cells, diminished the incorporation of 32Pi into monucleotides. They also decreased ATP concentration, suggesting that fatty acids, their derivatives, or an unknown factor connected with lipolysis impaired oxidative phosphorylation. Insulin diminished the inhibitory action of lipolytic agents and restored ATP concentration.