Agonist-dependent AT(4) receptor internalization in bovine aortic endothelial cells

Recent studies have characterized a specific binding site for the C-termina l 3-8 fragment of angiotensin II (Ang IV). In the present study we looked a t the internalization process of this receptor on bovine aortic endothelial cells (BAEC). Under normal culture conditions, BAEC efficiently internaliz ed I-125-Ang IV as assessed by acid-resistant binding. Internalization of I -125-Ang IV was considerably decreased after pretreatment of cells with hyp erosmolar sucrose or after pretreatment of BAEC with inhibitors of endosoma l acidification such as monensin or NH4Cl. About 50% of internalized I-125- Ang IV recycled back to the extracellular medium during a 2 h incubation at 37 degrees C. I-125-Ang IV remained mostly intact during the whole process of internalization and recycling as assessed by thin layer chromatography. As expected, internalization of I-125-Ang IV was completely abolished by d ivalinal-Ang IV a known AT(4) receptor antagonist. Interestingly, I-125-div alinal-Ang IV did not internalize into BAEC. These results suggest that AT4 receptor undergoes an agonist-dependent internalization and recycling proc ess commonly observed upon activation of functional receptors. (C) 1999 Wil ey-Liss, Inc.