Modelling of fluid-phase endocytosis kinetics in the amoebae of the cellular slime mould Dictyostelium discoideum. A multicompartmental approach.

Fluid-phase endocytosis (pinocytosis) kinetics were studied in Dictyostelium discoideum amoebae from the axenic strain Ax-2 that exhibits high rates of fluid-phase endocytosis when cultured in liquid nutrient media. Fluorescein-labelled dextran (FITC-dextran) was used as a marker in continuous uptake- and in pulse-chase exocytosis experiments. In the latter case, efflux of the marker was monitored on cells loaded for short periods of time and resuspended in marker-free medium. A multicompartmental model was developed which describes satisfactorily fluid-phase endocytosis kinetics. In particular, it accounts correctly for the extended latency period before exocytosis in pulse-chase experiments and it suggests the existence of some sorts of maturation stages in the pathway.