Increased binding of concanavalin a at the cell surface following exposure to thyroliberin

Abstract

Thyroliberin (THR) binds specifically to SD1 rat prolactin cells and increases prolactin release. THR-induced modifications of surface membrane of intact SD1 cells were looked for, using concanavalin A (Con A) as a probe. At the electron microscope level the binding was restricted to the cell surface. Preexposure of the cells to TRH (27 nM) for 30 min at 37°C increased the binding of Con A by 28–120%. Such an increase was not observed with low doses of TRH (13.5 and 2.7 nM) nor after only a 10-min exposure to 27 nM TRH. This effect is specific for TRH; it was not observed with other peptides. Simultaneous exposure to Con A and [ 3H]TRH did not alter [ 3H]TRH binding, but preexposure to Con A reduced the [ 3H]TRH binding by 10%, which may be due to steric hindrance. It is concluded that TRH induces an increased exposure of surface membrane glycoproteins in intact SD1 cells.