Microtubule--and microfilament--disrupting drugs and melanosome migration in melanophores of Papiliochromis ramirezi (Cichlidae, Teleostei).

We report here the effects of cytochalasin B, colchicine and vinblastine on melanosome migration in Papiliochromis ramirezi melanophores. Melanosome migration was not affected by 2 X 10(-5) M cytochalasin B. On the other hand, the aggregation, usually elicited by 10(-6) M norepinephrine, was completely inhibited by simultaneous treatment with 10(-3) M colchicine and cold (0-3 degrees C). Same results were obtained with 10(-3) M vinblastine. Lower concentrations of colchicine had no effect on granule aggregation. However, the aggregation in 50% of the melanophores was still blocked by 10(-5) M vinblastine, whereas 10(-7) M vinblastine was ineffective. Melanosome dispersion usually elicited by 10(-3) M theophylline was significantly accelerated by 10(-3) M colchicine, but delayed by 10(-3) M vinblastine. Lower concentrations of both agents had no effect on pigment dispersion. Therefore our results strongly suggest that microtubule structural integrity is essential to P. ramirezi melanosome displacements. As cytochalasin B had no effect on pigment migration, actin-like microfilaments might be either non-related to granule motion or absent in these chromatophores.