Endothelin–1 Aggravates Glutamate–induced Retinal Cell Death Through ETA Receptors

Abstract

Abstract: : Purpose: Effects of endothelin–1 (ET–1) on retinal neurons have not been fully determined. Because of its potent and long–lasting vascular effects, we performed in vitro studies using cultured retinal neurons to determine the direct actions of ET–1 and investigated the modification by ET–1 on glutamate–induced death of retinal neurons. Methods: Cultured retinal neurons from fetal rats were exposed to glutamate (1.0 mM) alone or glutamate with ET–1 (10^–10–10^–7M) for 10 minutes. Neuronal death was assessed by either the trypan–blue exclusion method or TUNEL assay 2, 6 and 24 hours after exposure. Effects of an addition of BQ–123 (an ET_A receptor antagonist) and BQ–788 (an ET_B receptor antagonist) in combination with ET–1 were also evaluated. Results: Brief exposure to ET–1 with glutamate caused further significant increase in retinal neuronal death compared to the cells exposed to glutamate alone; a significant deterioration 24 hours after exposure was achieved at doses of 10 nM and higher (P<0.05, Dunnett), while brief exposure of neurons to up to 1.0 µM ET–1 alone did not cause any delayed cell death of neurons. BQ–123 (10 nM) suppressed enhancement of retinal toxicity caused by ET–1 (10 nM), while BQ–788 had no observable effects. Conclusions: These results indicate that ET–1 aggravates glutamate–induced retinal cell death through ET_A receptors. Effects of ET–1 on the Ca²⁺ channels will also be discussed.

Keywords: neuropeptides • retinal culture • pathobiology