Angiotensin II receptor binding and actions in NG108-15 cells

NG108-15 cells were grown in culture to confluency and membranes were prepared from the cells to test for the presence of angiotensin II (Ang II) receptors using 125I-sarcosine1, isoleucine8 angiotensin II (125I-SI Ang II). These radioligand binding studies indicated a single class of binding sites with high affinity (KD = 221 +/- 54 pM) that were saturable (Bmax = 27.2 +/- 1.6 fmol/mg protein) and showed characteristic specificity (SI Ang II greater than Ang II greater than Sar1Thr8 Ang II greater than Ang III greater than Ang I greater than des Phe8 Ang II greater than des Asp1, Arg2, Val3 pentapeptide Ang II). To see if these putative receptor binding sites were associated with a functional response, the effect of Ang II on phosphatidylinositide (PtdIns) hydrolysis, expressed as inositol monophosphate (IP1) formation in intact NG108-15 cells preloaded with 3H-myoinositol, was determined. Ang II inhibited IP1 formation up to 35% below the basal rate in a dose related manner. The inhibition of PtdIns hydrolysis was prevented by pre-exposure of the cells to SI Ang II, an Ang II receptor antagonist. These results indicate that undifferentiated NG108-15 cells possess Ang II receptors that mediate a reduction in PtdIns hydrolysis.