Receptor mechanisms in fish chromatophores--VI. Adenosine receptors mediate pigment dispersion in guppy and catfish melanophores.

Using the guppy, Lebistes reticulatus, and the siluroid catfish, Parasilurus asotus , the effects of purine and pyrimidine derivatives on the movement of melanophores were studied. All the substances tested did not aggregate pigment within melanophores. Adenosine and adenine nucleotides were very effective in dispersing melanosomes within the cell, although adenine itself lacked such action. Derivatives of other purines than adenine and of pyrimidines did not disperse melanosomes. The pigment dispersion induced by adenine derivatives was specifically antagonized by methylxanthines. It was concluded that adenosine receptors are present on the melanophore membrane, which take part in the darkening reaction of fishes.