Taxol transport in Taxus baccata cell suspension cultures

Taxol transport in Taxus baccata L. cell suspension cultures was studied using 〚14C〛-taxol as a tracer. The time course of uptake showed a saturable absorption that reached a maximum within 20 min. The uptake depended on its exogenous concentration and its accumulation was highly stimulated in the presence of 10–15 μM exogenous taxol. The absorbed molecule was found to localise both in the cell walls (20 %) and in the cell protoplasts (80 %), suggesting an accumulation within the vacuoles. Taxol uptake was strongly inhibited by Na-orthovanadate and verapamil, while Ca2+ was found to be one of the factors required for the active absorption of the molecule, since in the absence of this cation, the uptake was reduced by about 40 % and occurred mainly through a non-energy dependent mechanism. Taxol release into the culture medium was demonstrated not to depend on cell lysis, occurred through a mechanism that reached its maximum after 10–15 min and was strongly enhanced by treatment with Na-orthovanadate and verapamil, although the effect was found to be transient.