Department of Biomolecular Science, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274, Japan
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In many species of teleosts, and in zebrafish (Brachydanio rerio) in particular, endothelin-1 (ET-1) caused aggregation of pigment within melanophores in a dose-dependent manner. ET-1 appeared to act directly on the melanophores since denervated melanophores responded to the peptide quite similarly to the normally innervated cells. Alpha-adrenergic blockers, namely, phentolamine and tolazoline, and a muscarinic cholinergic blocker, scopolamine, did not interfere with the action of ET-1 on melanophores. Contrary to our expectations, BQ-123, an inhibitor of mammalian ET-1 receptors (ETA receptors), did not block the action of ET-1 on melanophores. Presumably, teleostean ET receptors have very different pharmacological characteristics from those of mammalian species. In many fishes, ET may be involved in the subtle and delicate modification of hues and patterns of the integument that are associated with their elaborate and effective chromatic strategies for survival.