Specific receptor for angiotensinogen on human renal cells

BackgroundWe recently demonstrated the existence of an angiotensinogen (AGT) receptor on placental cells. It has been established that there is a tissue-specific renin–angiotensin system (RAS) in the human kidney. This study focused on whether human renal proximal tubule epithelial cells possessed an AGT receptor.MethodsHuman renal proximal tubule epithelial cells were cultured in plastic wells. Binding assays were carried out by adding iodinated angiotensinogen (125I-AGT) to each culture well, with or without unlabeled AGT. The cells were washed, lysed, and the radioactivity was measured.ResultsHuman renal proximal tubule epithelial cells bound 125I-AGT in a time-dependent manner. This binding was competitively and specifically inhibited by unlabeled AGT. Bound 125I-AGT was competitively displaced by AGT. Acid washing removed 30% at 8 h, indicating that 70% bound AGT had been internalized. Scatchard plot binding analysis showed that the identified AGT receptor possessed a single class of high-affinity binding sites (Kd = 1.73 nmol, Bmax = 23.39 pmol/106 cells).ConclusionThe results of this study provide evidence for the presence of an AGT receptor on human renal proximal tubule epithelial cells. Our finding suggests that the AGT receptor may be an integral component of the renal RAS.