The influence of microtubule integrity on plasma membrane fluidity in L929cells

The aim of this work was to examine the possible influence of the integrity of the microtubule network on the plasma membrane fluidity of L929 mouse f ibroblasts. The L929 cell line was selected for the ease of culture and the stability of its characteristics. The cells were treated with colchicine, nocodazole and vinblastine, three microtubule-depolymerizing drugs, at vari ous concentrations and for various times. Membrane fluidity was assessed fr om fluorescence depolarization measurements with the plasma membrane probe TMA-DPH. Each of the drugs induced a significant, dose-dependent decrease i n fluorescence anisotropy. The effect levelled off (5-7% decrease) after si milar to 90 min of treatment, and could be unambiguous ly interpreted as re sulting from an increase in membrane fluidity. The cumulative action of the drugs did not significantly increase the effect. The effects of colchicine and nocodazole could be reversed by incubation in drug-free medium, but no t that of vinblastine. The results are discussed in correlation with the ki netics of the three drugs interaction with tubulin or microtubules. It is c oncluded that the microtubule integrity contributed to the high plasma memb rane lipidic order, but less than other factors, like the lipid composition and the cholesterol content.