Endothelins disperse light-scattering organelles in leucophores of the medaka, Oryzias latipes.
Fujita T. Fujii R .
Dep. Biomol. Sci., Fac. Sci., Toho Univ., Miyama, Funabashi, Chiba 274,
Japan.
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 concentrations being less than 100 pM, with EC-50 value about 8.3-8.4 nM. Endothelins act directly on the leucophores, since denervated cells responded to the peptides quite similarly. Phentolamine, an alpha-adrenergic blocker, propranolol, a beta-adrenergic blocker, and BQ-123, an inhibitor of mammalian ET-A receptor, did not interfere with the action of ETs. By contrast, BQ788, 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.