Electron microscopic demonstration of glucocorticoid recognition sites on isolated rat hepatocytes

Ultrastructural evidence is presented for the presence of membrane-bound glucocorticoid recognition and binding sites. Corticosterone was derivatized at 3 different positions and coupled covalently to bovine serum albumin (BSA). All three derivatives competed for binding of [3H]corticosterone by isolated rat hepatocytes. The most effective competitor, corticosterone-succinate-BSA (CSB), was adsorbed onto colloidal gold particles (CSB-gold, 17 +/- 3 nm dia). When isolated rat hepatocytes or mouse pituitary tumor cells (AtT 20) are incubated with CSB-gold, specific binding in the microvilli-rich region of these cells is seen. This binding of CSB-gold is reduced by about 50% in the presence of unlabelled CSB or corticosterone.