Variation in melanosome numbers in cultured B‐16 melanoma cells

Melanosomes from B‐16 mouse melanoma cells in culture were isolated by treatment of pigmented cells with 2% SDS, sonication, and heating at 100°C. The total number of melanosomes in cultures of B‐16 mouse melanoma cells increased exponentially during the rapid phase of sigmoid growth. The numbers of melanosomes per cell decreased during rapid phase of growth, and repigmentation was observed only when the cultures attained the stationary growth phase. BUdr at a minimum concentration of 0.5 μg/ml decreased both cell growth and numbers of melanosomes per cell, and completely inhibited repigmentation following a period of active growth. Cells cultured in 0.1 μg/ml BUdr grew at the same rate as untreated cells but contained fewer melanosomes/cell and lower total numbers of melanosomes during the late stages of the growth cycle.