[Plasma membrane of thymocytes--home of specific glucocorticoid binding sites]

The incubation of rat thymocytes with 3H-cortisol in the presence of cortisol immobilized on polyvinylpyrrolidone (PVP-GC) produces a decrease in 3H-cortisol uptake by these cells. PVP-GC is shown to compete with cortisol for specific binding sites on thymocytes, without penetrating into cells. It is therefore, concluded that plasma membranes of thymocytes contain specific glucocorticoid binding sites.