IDENTIFICATION OF ENDOTHELIN RECEPTOR SUBTYPE (ET(B)) IN HUMAN CEREBRAL-CORTEX USING SUBTYPE-SELECTIVE LIGANDS

Specific endothelin (ET) binding sites were characterized in membranes prepared from human cerebral cortices using binding assay and cross-l inking analysis. The presence of immunoreactive (IR) ET-1 was studied by radioimmunoassay. Saturation binding experiments revealed that the K(D) and B(max) for I-125-ET-1 and I-125-ET-3 to membranes from gray m atter were 25 +/- 6 pM and 115 +/- 15 fmol/mg of protein and 24 +/- 5 pM and 108 +/- 13 fmol/mg of protein, respectively. Similar results we re obtained for white matter. In the presence of 10 nM sarafotoxin-6c, which is selective for ET(B) receptors, I-125-ET-1 and I-125-ET-3 bin ding was totally abolished. However, in the presence of 1 muM BQ123, w hich is selective for ET(A) receptors, both bindings were not affected . These results suggest that the human cerebral cortex contains only E T(B) receptors. Cross-linking of I-125-ET-1 and I-125-ET-3 to membrane s with disuccinimidyl suberate resulted in the labeling of two bands o f 48 and 31 kDa. Concentrations of IR-ET-1 in the gray and white matte r were 7.0 +/- 3.2 and 2.5 +/- 1.7 fmol/g wet weight, respectively. Th e demonstration of high-affinity ET(B) receptors and the presence of I R-ET-1 suggest that the peptide may act as a neurotransmitter or neuro modulator in the human cerebral cortex.