The endothelin receptors that mediate aggregation of pigment in fish melanophores

Abstract

A study was made of effects on the melanophores of several teleosts of three isopeptides of mammalian endothelin (ET), namely, ET-1, ET-2, and ET-3. In all the species examined, these peptides induced the aggregation of pigment within the melanophores. Chemically denervated melanophores also responded to ETs quite normally. Thus, ETs may act directly on the cells. Quantitative studies on the dark chub and zebrafish indicated that the response was concentration-dependent, and that the three peptides were almost equipotent. Sarafotoxin S6c, a specific agonist of the mammalian ET A receptor, also effectively induced the aggregation of pigment in a concentration-dependent manner. IRL 1620, another specific agonist of the ET B receptor, also induced the aggregation of pigment, but only at higher doses. BQ- 123 and TTA-386, potent selective antagonists that bind to mammalian receptor of the ET B type, did not interfere with the pigment-aggregating actions of ETs, whereas BQ-788, an ET B receptor-selective antagonist, strongly inhibited the action of ETs. It appears, therefore, that the receptors for ET that mediate the aggregation of pigment in fish melanophores resemble those of the mammalian ET B type.