Characterization of regulation of thyrotropin (TSH) receptor function in thyroid plasma membrane: interaction between TSH receptor function and activation of adenosine 3',5'-monophosphate-dependent protein kinase.

The changes in the characteristics of thyrotropin (TSH) binding to thyroid plasma membranes during the activation of cyclic AMP-dependent protein kinase in the membranes were studied. Preincubation of thyroid plasma membranes with TSH or cyclic AMP reduced the maximal binding capacity but increased the association rate for TSH binding. In double reciprocal analysis, a marked reduction of the total number of binding sites and association constant was observed in the membranes treated with cyclic AMP. These reductions were also observed in the membranes preincubated with buffer alone. The degree of these reductions, however, was greater in the membranes pretreated with cyclic AMP. During incubation of the membranes with buffer alone, cyclic AMP formation (activation of adenylate cyclase) was observed though the degree of the formation was lower than that induced by TSH. The results suggested that not only TSH receptor release from thyroid plasma membrane but also the modification of TSH binding activity in the membrane is produced by cyclic AMP-dependent protein kinase.