Membrane vesicles in the study of transport processes: a critical analysis of the experimental procedure.

A critical analysis of the use of membrane vesicles in the study of cotransport processes is presented. Transport experiments were simulated according to two different models, stressing those conditions that seemed more relevant in affecting the measurements. In particular, we observed that the experimental Vmax values were underestimated. This underevaluation depended on the incubation time employed to measure the initial uptake rate and on the time necessary to wash the vesicles. Also the temperature and the composition of the washing solution, together with the Q10 of the transport process taken into consideration, had a consistent influence on the uptake. All the above mentioned effects were affected by the vesicle volume: the smaller the volume, the greater the underestimate of the uptake. This theoretical analysis underlines, on the one side, that the experimental data should be interpreted with some caution, on the other, that the examined procedure allows an internal check of its validity by adopting suitable simulations of the experiments. The use of the presented models as a tool for the planning and the critical analysis of the experimental results is suggested.