Characterization of an angiotensin binding site in rabbit renomedullary interstitial cells in tissue culture: correlation with prostaglandin biosynthesis.

High affinity binding sites for angiotensin II have been identified and characterized in rabbit renomedullary interstitial cells in tissue culture. Binding studies were performed using monoiodinated angiotensin II of high specific activity; the angiotensinase inhibitors dithiothreitol and phenylmethylsulfonylfluoride were added to the incubation medium to retard degradation of the labeled hormone. Uptake of 125I angiotensin II was maximal at pH 7.4 and Scatchard analysis indicated a single binding site with a KD of 3.1 nM. Binding to a particulate preparation of the cells was rapid and reversible. Competition for binding by angiotensin II analogs correlated with their biologic potencies: (Sar1Ala8) AII greater than AII greater than (desAsp1) AII greater than greater than 3-8 hexapeptide. The 1-7 heptapeptide was completely ineffective in displacing the labeled angiotensin II from its binding sites. Angiotensin II directly stimulated prostaglandin (PG) biosynthesis by the renomedullary cells in tissue culture; the concentration of angiotensin II that resulted in half maximal stimulation of PG biosynthesis (6.5 nM) was similar to the concentration of angiotensin II that resulted in half maximal occupancy of binding sites (3.1 nM). These results suggest that the renomedullary cells may provide a model homogeneous tissue for the study of the angiotensin receptor and the hormonal regulation of prostaglandin biosynthesis.