The Endothelin/Sarafotoxin‐Induced Increase of the Proliferation of Undifferentiated and DMSO‐Differentiated GEM‐81 Goldfish Erythrophoroma Cells is Mediated by ETB Receptors

Endothelins (ETs) and sarafotoxins (SRTXs) have been reported to exert ET_B‐mediated effects on vertebrate pigment cells. GEM‐81 cell line, a red pigment cell‐derived cutaneous tumor of the teleost Carassius auratus, expresses ET_B receptors and can be differentiated with 1.5% DMSO treatment, thus constituting an useful model to investigate ET and SRTX effects on cultured fish pigment cells. Our aim was to characterize the pharmacology and biological effects mediated by ET receptors in DMSO‐differentiated and undifferentiated cells. ET subtype receptors and their respective Ki values in both cell types were determined by competitive binding assays using ¹²⁵I ET‐1 and BQ‐485 (an ET_A antagonist) or BQ‐788 (an ET_B antagonist). BQ‐788, but not BQ‐485, significantly reduced ¹²⁵I‐ET‐1 binding in both cell types, with similar low (Ki > nM) affinities. To determine the proliferation effects of ETs/SRTXs, cells were treated for 72 h with the hormones, and counted in a hemocytometer. The proliferation assays were repeated for SRTX S6c in the presence or absence of BQ‐788. The results demonstrated that, with the exception of ET‐1 (biphasic effect) and ET‐3 (no significant effect) in undifferentiated GEM‐81 cells, all the tested hormones induced increases in the proliferation of both types of cells. The hormones were equipotent in DMSO‐differentiated cells, which exhibited increased sensitivity to ETs, but not to SRTXs, as compared with undifferentiated cells. The BQ‐788 antagonistic effect was also exerted on the proliferation responses to SRTX S6c. These results corroborate the long and important evolutionary history of the ET/SRTX receptor system in vertebrate pigment cells.