Endothelins Disperse Light-Scattering Organelles in Leucophores of the Medaka, Oryzias latipes

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Mammalian endothelins (ETs : ET-1, -2 and -3) effectively disperse the light-scattering organelles (leucosomes) in leucophores of the medaka, Oryzias latipes, in a dose-dependent manner. They were almost equally effective, their minimal effective concentraitons being less than 100pM, with EC_<50> value about 8.3-8.4 nM. Endothelins act directly on the leucophores, since denervated cells responded to the peptices quite similarly. Phentolamine, an α-adrenergic blocker, propranolol, a β-adrenergic blocker, and BQ-123, an inhibitor of mammalian ET_A receptor, did not interfere with the action of ETs. By contrast, BQ-788, an inhibitor of the mammalian ET_B receptor, potently blocked the action of ETs. Sarafotoxin S6c and IRL 1620, both mammalian ET_B receptor-selective agonists, were also found to disperse leucosomes effectively, mimicking the effect of ETs. Thus, ETs may act through the mediation of specific receptors existing in the leucophores. Along with their recently disclosed actions on light-absorbing chromatophores, ETs may play an important role in the delicate and exquisite control of integumentary hues and patterns.