摘要：

The accumulation of [ 14C]tabernanthine by cell suspensions of Catharanthus roseus has been studied. [ 14C]Tabernanthine added in the culture medium rapidly enters the cells. A steady state equilibrium is reached after about 1 h with an accumulation ratio from 25 to 100. Evidences are presented for a diffusive uptake involving mainly the uncharged form of tabernanthine molecules. The charged form cannot cross membranes and is trapped into the acidic compartments of cells, e.g. the vacuole. In agreement with this model, the accumulation ratio of [ 14C]tabernanthine (p K a = 8.1) inside the cells has been found to be higher than the one of [ 14C]ajmalicine (p K a = 6.3) but lower than the one of [ 14C]tryptamine (p K a = 10.2). Furthermore, this accumulation is modulated by pH-values inside and outside the cells. When the pH of the external medium is decreased, or when the intracellular pH is increased, the accumulation of tabernanthine is decreased. The mechanisms of tabernanthine accumulation seem rather unspecific as Acer pseudoplatanus cells accumulate it in the same manner as C. roseus cells. However, the diffusion model described above cannot explain entirely the intracellular accumulation of tabernanthine. The hypothesis is made that a binding to intracellular components is also involved in the accumulation process.

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