RECEPTOR-BINDING AND BIOLOGIC ACTIVITY OF SYNTHETIC ET-1 PEPTIDES IN THE RETINAL PERICYTE

Purpose. The purpose of this study was to examine the effect of synthe tic endothelin (ET)-1 peptides with antigenic potential for binding an d biologic activity using an in vitro model of microvascular pericytes . Methods. All possible sequential hexapeptide fragments of endothelin s -1, -2, and -3 were synthesized on polyethylene rods and tested for reactivity with antibodies for ET-I and ET-3. The most highly antigeni c peptide ET-1[38] and the least antigenic ET-1[1-6], which gave low r eactivity in the enzyme-linked immunosorbent assay (ELISA), were synth esized. The C-terminal hexapeptide ET-1[16-21], which has been reporte d as an ETB receptor agonist but which gave no reactivity in the ELISA , also was investigated. The synthesized ET analogues were tested for receptor binding, inositol phosphate generation, and mitogenesis in bo vine retinal pericytes. Results. ET-1[16-21] partially inhibited both [I-125]-ET-1 and [I-125]-ET-3 binding at high concentrations, as did E T-1[1-6]. In contrast, ET-1[3-8] displaced labeled ET-1 binding but no t labeled ET-3 binding. None of the peptides had any significant mitog enic or second-messenger responses when compared to those elicited by the full ET-1 molecule. Conclusions. The result of the current work sh ows that the sequence, ET[3-8], is involved in isopeptide-specific bin ding to ETA receptors, but it suggests that other regions of the molec ule are necessary for full bioactivity in microvascular pericytes.