Subcellular distribution and phosphorylation state of insulin receptors from insulin- and isoproterenol- treated rat adipose cells

Rat adipose cells treated with insulin followed by isoproterenol exhibit a change in glucose transporter intrinsic activity (lowered maximal activity) and a decrease in insulin sensitivity (rightward shift of the concentration-response curve) when assayed for 3-O-methylglucose transport. To investigate the latter phenomenon, the distribution and phosphorylation state of insulin receptors was examined. Isoproterenol augmented the effect of insulin cell surface receptors by 20-30%. These receptors were recovered in microsomal fractions. Isoproterenol also markedly reduced insulin-stimulated [³²P]phosphate incorporation into the plasma membrane receptor β-subunit. These effects may account for the effect of isoproterenol to decrease the sensitivity of the glucose transport response to insulin.