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In dermal melanocytes of Rana pipiens, colchicine is known to produce a gradual, dosage-dependent dispersion of melanin granules, irreversible over several hours. This effect is potentiated by a number of chemical agents that normally produce a reversible dispersion of granules. In the present study we examined the effect of high hydrostatic pressure on changes induced in melanocytes by colchicine.In finger's solution, samples of skin from a single frog were incubated for 30 minutes at room temperature with or without colchicine, 9 X M. Then two samples, one of which had been pretreated with colchicine, were successively subjected to 12,000 psi for one hour at 25 to 26°C. The degree of dispersion of melanin granules in melanocytes was observed before, during and after the period of pressure.In frog skin pretreated with colchicine, the usually gradual, irreversible dispersion of melanin granules in rnelanocytes was potentiated, Since high pressure i s known to produce solational changes in protoplasm, such changes may accompany dispersion of melanin granules in melanocytes. If this be so, then sol-gel equilibria may be important in the action of dispersing and aggregating agents, many of which are hormones and other physiologically active agents. Finally, the present study supports the hypothesis that colchicine shifts protoplasmic sol-gel equilibria toward a less gelated condition.

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