Control of chromatophore movements in dermal chromatic units of blue damselfish--II. The motile iridophore.

The mechanism regulating the movements of the unique motile iridophores of the blue damselfish, Chyrsiptera cyanea, was studied. The reaction in which the cells become reflective to light rays of longer wavelength, i.e. from the near u.v. region to the green region, was designated as the "coloring response", while the reverse process was labeled the "clearing response". Both nervous stimuli and adrenergic agonists gave rise to the coloring response, which could be antagonized by alpha adrenolytic agents. The clearing response was accelerated by adenosine and inhibited by theophylline. None of the hormonal substances tested had any effect on the motile response of the cells. It was concluded that the motile iridophores are solely under the control of the sympathetic adrenergic system, and that the co-transmitter, adenosine, may function to antagonize quickly the true transmitter-induced colored state of the cells.