Characterization of a high affinity, guanine nucleotide sensitive angiotensin receptor on differentiated neuroblastoma-glioma hybrid cells (NG108-15)

The binding characteristics of [¹²⁵I]angiotensin II (ANG II) to membranes prepared from undifferentiated and differentiated neuroblastoma × glioma hybrid cells (NG108-15) were investigated. Scatchard analysis revealed the existence of high and low affinity sites in differentiated cells, but only a low affinity site in undifferentiated cells. Similarly, self-displacement studies revealed competition to a single low affinity site in undifferentiated cells, and to high and low affinity sites in differentiated cells. Angiotensin III (ANG III) displaced high affinity binding in differentiated cells but did not displace low affinity binding in either differentiated or undifferentiated cells. Furthermore, 5- guanyl imidodiphosphate (GPP(NH)P) inhibited [¹²⁵I]ANG II binding to differentiated cells, in a dose-dependent fashion, but had no effect on binding to indifferentiated cells. These findings suggest that the high affinity site represents a G-protein linked receptor with approximately equal affinities for ANG II and ANG III. We hypothesize that the low affinity site represents a non-specific membrane-bound aminopeptidase.