Endothelin binding to NG108-15 cells: evidence for conventional ETA and ETB receptor subtypes and super-high affinity binding components

The endothelin (ET) peptides have been identified in the CNS, but there is a paucity of information on their physiological roles. NG108-15 cells, a clonal strain of a neuroblastoma x glioma hybrid cell line, have been widely used in neurobiological research since they retain certain differentiated properties of the non-transformed parental cells. It is known that NG108-15 cells respond to the ET peptides, but only limited information is available on the characterization of the ET receptors that mediate these effects. The present study was designed to identify the type(s) of ET receptors on NG108-15 cells in a proliferative state by competitive binding assays using 125I]ET-1 as the radiolabelled ligand and the receptor-selective ligands. ET-1, ET-3, BQ-123, sarafatoxin-6-c and Ala1,3,11,15]ET-1. The results suggested the presence of conventional ETA and ETB receptor subtypes, with ETA in excess over ETB. These findings were consistent with the results of Northern analysis in that mRNAs encoding the ETA and ETB receptor subtypes were identified in NG108-15 cells, with a preponderance of ETA to ETB. Of considerable interest was the observation of other ET-binding components with much higher affinities than the conventional receptors. It remains to be demonstrated if these particular binding components are functional and represent differ gene products or arise from association of the conventional ETA and ETB receptor subtypes with themselves or other structures, e.g. proteins or lipids, of CNS origin.