Vinblastine but not other microtubule inhibitors block transferrin endocytosis and iron uptake by reticulocytes.

The antimicrotubule reagents, colchicine, griseofulvin, nocodazole, podophylotoxin and taxol had no effect on transferrin endocytosis or iron uptake by rabbit or rat reticulocytes but were inhibitory when used at high concentrations with rat fetal liver erythroid cells. The results imply that microtubules do not have a role in endocytosis and iron uptake by reticulocytes but may have a permissive role in the fetal cells. The only reagent found to inhibit iron uptake by reticulocytes was vinblastine. It was shown to act by inhibiting the endocytosis of transferrin. It is concluded that this effect is not the result of an interaction with microtubules, but may result from a non-specific action on the cell membrane or a more specific effect, such as inhibition of calmodulin.