Angiotensin AT2 receptor degradation is prevented by ligand occupation

A substantial increase in [125I]Sar1, Ile-Angiotensin II binding activity can be observed 24 hours after treatment of R3T3 cells with AT2 receptor agonists and antagonists. An increase in the radioligand binding activity, although less profound, can also be observed 6 hours after AT2 receptor ligand treatment, on fetal human kidney cells expressing a recombinant human AT2 receptor. However, the increase in radioligand binding activity cannot be detected unless the ligands are removed from the cell surface by an acid-glycine (pH 3) wash, just prior to the binding assay. Interestingly, an acid-glycine wash 24 hours prior to the binding assay causes a dramatic decrease in the radioligand binding activity on untreated R3T3 cells. This decrease, which was prevented by angiotensin II treatment, suggests the existence of an unknown endogenous factor which, like the AT2 receptor ligands, seems to prevent AT2 receptor degradation.