title: [H]BQ-123 binding to native endothelin ET(A) receptors in human astrocytoma 1321N1 cells and screening of potential ligands.
abstract: Endothelin ET(A) receptors on the human astrocytoma 1321N1 cell line were characterized in radioligand binding studies using the ET(A)-selective antagonist radioligand [(3)H]BQ-123. A membrane preparation of the cell line showed a high expression level of ET(A) receptors (B(max) = 128 fmol/mg protein). The K(D) value for [(3)H]BQ-123 (K(D) = 2.29 nmol/l) was comparable to that previously determined at the human neuroblastoma cell line SK-N-MC. The specific labeling of ET(A) receptors on astrocytoma 1321N1 cells by [(3)H]BQ-123 was confirmed by determining the rank order of potency of a series of agonists and antagonists. A competition assay for the screening of potential ET(A) ligands was established and a series of new disubstituted imidazo[1,2-c]pyrimidine and pyrimido[1,6-a]pyrimidine derivatives was investigated. Moderate ET(A) affinity was detected for several derivatives [30-40% inhibition of [(3)H]BQ-123 binding (3 nmol/l) at a concentration of 10 micromol/l]. Astrocytoma 1321N1 cells natively express relatively high levels of ET(A) receptors. They are useful for the screening of potential ET(A) ligands in radioligand binding assays with [(3)H]BQ-123.
authors.affiliation: Pharmaceutical Institute, Pharmaceutical Chemistry Poppelsdorf, University of Bonn, Bonn, Germany.
authors.forename: Kerstin J
authors.initials: KJ
authors.lastname: Griessmeier
authors.forename: Christa E
authors.initials: CE
authors.lastname: Muller
mesh_terms: D001254:Astrocytoma; D001667:Binding, Competitive; D045744:Cell Line, Tumor; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D010456:Peptides, Cyclic / Q000378:metabolism*; D011485:Protein Binding; D011743:Pyrimidines / Q000378:metabolism*; D011869:Radioligand Assay; D044022:Receptor, Endothelin A / Q000378:metabolism*; D014316:Tritium
chemical_list: D008024:Ligands; D010456:Peptides, Cyclic; D011743:Pyrimidines; D044022:Receptor, Endothelin A; D014316:Tritium; C072247:cyclo(Trp-Asp-Pro-Val-Leu)