Light-induced pigment aggregation in xanthophores of the medaka, Oryzias latipes

The response mechanism of medaka xanthophores to light was examined at the cellular level. Innervated and denervated xanthophores of adult medakas res ponded to light (9,000 lux) within 30 sec by pigment aggregation, and this aggregation was not mediated through alpha-adrenoceptors on the cell membra ne. Maximum sensitivity to light was at wavelengths of 410-420 nm, and the direct effect of light was reversible. Xanthophore responsiveness to light in summer was higher than that in winter. Ca2+ and calmodulin were not invo lved in the response, but rather, an important role for cAMP and phosphodie sterase (PDE) was suggested. It seems likely that photoreception by visual pigment which is sensitive to light at wavelengths of 410-420 nm increases PDE activity, probably via a G-protein, such as occurs with visual cells in the retina, which causes a decrease in levels of cytosolic cAMP, in turn l eading to pigment aggregation within medaka xanthophores.