Identification and Regulation of Angiotensin II Receptor Subtypes on NG108‐15 Cells

NG108-15 cells, a neurally derived clonal cell line, express various components of the renin-angiotensin system and thus serve as a model of the cellular action of angiotensin (Ang) II. NG108–15 cells contain a high-affinity binding site for Ang II, with a Kd of 1.1 nM and a Bmax of 6.5 fmol/mg protein. Ang peptides competed for 125I-Ang II binding with an order of potency of Ang II>Ang-(2–8)≫Ang-(l–7). The subtype 1 (or B)-selective Ang II receptor antagonist DuP 753 as well as [Sar1,Ile8]Ang II and [Sar1,Thr8]Ang II competed for Ang II binding with high affinity, whereas the subtype 2 (or A)-selective Ang receptor antagonist CGP 42112A was partially effective only at a 300-fold higher concentration. When NG108-15 cells were induced to differentiate by treatment with dibutyryl cyclic adenosine 3′,5′-monophosphate, the density of Ang II receptors increased dramatically, with little change in affinity (1.1 versus 4.2 nM) or competition by Ang peptides. In marked contrast to undifferentiated cells, CGP 42112A became a potent competitor (IC50, 1 nM) for the majority (90–95%) of Ang II binding, whereas DuP 753 competed for only 5–10% of the binding sites. Ang II caused a dose-dependent mobilization of cytosolic Ca2+; in undifferentiated NG108-15 cells through activation of phospholipase C and the production of Inositol 1,4,5-trisphosphate. In these cells, Ca2+ mobilization was blocked by either DuP 753 or the sarcosine Ang II analogues, whereas CGP 42112A was ineffective. Ang II also mobilized intracellular Ca2+ in differentiated NG108-15 cells. This effect was blocked by either DuP 753 or the sarcosine analogues but not by CGP 42112A. These data show that both undifferentiated and differentiated NG108-15 cells contain a subtype 1 Ang II receptor that activates phospholipase C and mobilizes intracellular Ca2+. However, in differentiated NG108-15 cells, the majority of Ang II receptors are subtype 2, suggesting that neuronal differentiation regulates the expression of subtype 2 receptors.