The effects of lumicolchicine, colchicine and vinblastine on pigment migration in fish chromatophores

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Abstract
The effects of lumicolchicine, colchicine, vinblastine and cold temperature on the pigment migration in melanophores and xanthophores of Fundulus heteroclitusand Oryzias latipeswere examined by light and electron microscopy. Xanthophores of both species which contain numerous microfila‐ments and a poorly developed microtubule system were extremely sensitive to the alkaloids. Lumicolchicine and colchicine induced irreversible dispersion while vinblastine caused permanent aggregation of the pigments. Treatment in lumicolchicine or colchicine at 5 mM for 60 minutes did not disrupt micro‐tubules of melanophores to an appreciable degree, however, melanosome aggre‐gation was partially inhibited by these drugs in Oryzias. When melanophores were kept in the cold in the presence of colchicine at 1 mM, almost all micro‐tubules were disrupted and their repolymerization at room temperature was nearly completely inhibited by colchicine. These melanophores lacking in mi‐crotubules responded to epinephrine with slow aggregation. Vinblastine at 0.1 mM induced partial aggregation of melanosomes and disruption of micro‐tubules but most melanophores were still able to respond with pigment migra‐tion. Vinblastine at 1 mM made all melanophores punctate and immobile. Large vinblastine‐induced crystals were frequently seen in the dendritic proc‐esses. The results of the present investigation suggest that cytoplasmic micro‐tubules in fish melanophores facilitate melanosome migration only in di‐rectional orientation and appear not to be responsible for the motive force.