The role of microtubules in pinocytosis. Inhibition of fluid-phase pinocytosis in the rat visceral yolk sac by mitoclasic and related agents.

Colchicine, demecolcine and vinblastine all effectively inhibited the pinocytic capture of 125I-labelled poly(vinylpyrrolidone) by rat visceral yolk sacs cultured in vitro. Complete inhibition did not occur until 2-3h after addition of mitoclasic agent and this delay appeared to be related to the mechanism of drug-microtubule interaction rather than any difficulty of drug permeation into cells. Inhibition of pinocytosis by demecolcine was reversible, whereas inhibition by colchicine or vinblastine was not. In terms of dose-response demecolcine was slightly more effective than colchicine, but both were considerably more active than trimethylcolchicinic acid. Of the nine benzimidazoles tested for ability to inhibit pinocytosis, four severely retarded uptake and three were partially inhibitory.