[Mouse cell accumulation of Colcemid and colchicine in tissue culture]

Kinetics of the uptake of 3H-colchicine and 3H-colcemid by mouse transformed L cells has been studied. The amounts of colchicine and of colcemid, accumulated by cells during a long-term incubation appeared to be equal; however, the initial uptake rates being higher for colcemid. The rates of the efflux of 3H-colchicine and 3H-colcemid were also different. After a 3 hours incubation of cells in antitubulin-free medium, the cells retain as much as 70% of colchicine, and only 10% of colcemid. It is known that colchicine does not bind tubulin at 0 degrees C; a colchicine analog lumicolchicine does not bind tubulin at any temperature. We have shown that the rate of 3H-lumicolchicine efflux at 37 degrees C is very rapid. The same was true for colchicine, if the incubation with the drug was performed at 0 degrees. We suggest that the difference in the rates of influx and efflux between colchicine and colcemid may be due to differences in their capacities of binding tubulin and dissociating from it.