Evidence for glucocorticoid transport into AtT-20 cells. Selective effect of a sulfhydryl inhibitor on uptake.

The purpose of these experiments was to determine if membrane-mediated glucocorticoid uptake by the AtT-20 cell was sensitive to the sulfhydryl group inhibitor, p-chloromercuriphenylsulfonate (PCMPS). This agent was chosen because of its reported limited entry into the cell interior. Our experimentes showed that cells could be incubated with 1 mM PCMPS for 1 h before intracellular concentrations of the inhibitor were sufficient to affect the intracellular cytosol receptor. In contrast less than 15 min of treatment inhibited intact cell steroid uptake. The inhibition was completely reversed by dithiothreitol. These studies show inhibition of glucocorticoid uptake under conditions which do not affect the intracellular receptor and infer that the AtT-20 cell membrane-mediated uptake mechanism for glucocorticoids contains sensitive sulfhydryl groups.