SPECIFIC BINDING-SITES FOR I-125 ENDOTHELIN-1 IN THE PORCINE AND HUMAN SPINAL-CORD

Specific binding sites for I-125-endothelin-1 (I-125-ET-1) in the spinal cord were investigated using quantitative receptor autoradiographic and chemical cross-linking methods. The binding sites were highly concentrated in porcine and human spinal cord areas corresponding anatomically to the dorsal horn (Rexed's laminae I-III), an area around the central canal (lamina X) and the principal part of the intermediolateral nucleus (IMLp). The localization of the binding sites differed from those of I-125-omega-conotoxin GVIA (I-125-CgTx) and I-125-Bolton-Hunter substance P (I-125-BH-SP), with the exception that the IMLp shared I-125-ET-1 with I-125-CgTx and I-125-BH-SP binding sites. Specific I-125-ET-1 binding sites in the areas examined were characteristically single and of high affinity. There were no differences between the potencies of unlabeled ET family peptides, ET-1, ET-2, ET-3 and sarafotoxin S6b at inhibiting I-125-ET-1 binding to the areas. Chemical cross-linking studies showed that I-125-ET-1 and I-125-ET-3 mainly bound to a protein with molecular mass of 43 kDa in the porcine and human thoracic spinal cord membranes. The present finding shows the neuronal significance of this newly discovered peptide in the spinal cord.