IDENTIFICATION OF CONVENTIONAL AND NOVEL ENDOTHELIN RECEPTORS IN SHEEP CHOROID-PLEXUS CELLS

Previous studies have demonstrated the presence of super-high affinity endothelin receptors with apparent K-d's on the order of pM in differ ent brain tissues. This study was designed to characterize, in detail, the receptors present in SCP cells, a non-transformed sheep choroid p lexus cell line. Competitive binding assays with receptor-selective li gands indicated the presence of at least three classes of binding site s: a conventional receptor of the ET(A) subtype with a K-d = 0.4 nM th at mediates an increase in intracellular levels of inositol 1,4,5-tris phosphate (IP3) in response to ET-1 and two additional sites with much higher binding affinities. The latter two sites are not coupled to th e common signal transduction pathways of IP3, cAMP and cGMP. Northern blot analysis confirmed the presence of only the ET(A) subtype mRNA in SCP cells. It remains to determined if the multiple binding sites are distinct gene products, multiple affinity states of a single receptor molecule or a result of cooperative association of one site with eith er the ligand or with other proteins.