Adenosine receptors mediate pigment dispersion in leucophores of the medaka, Oryzias latipes

Using the medaka, Oryzias latipes (orange-red variety), the mechanisms of action on leucophores of adenosine and adenine nucleotides, including cyclic AMP, were studied. All these substances were found to be very effective in dispersing leucosomes. Their pigment-dispersing action was antagonized by methylxanthines. These substances did not aggregate leucosomes. It was concluded that leucophores possess specific binding sites for adenosine, i.e. adenosine receptors, on the cell membrane, which mediate leucosome dispersion. Further, it was shown that even the action of an established intracellular second messenger, cyclic AMP, is primarily manifested through the receptors.