Kinetics of fluid-phase pinocytosis in Dictyostelium discoideum amoebae.
Kinetics of pinocytosis in Dictyostelium discoideum were investigated over an extended period of time (up to 6 hours) using fluorescein isothiocyanate (FITC)-dextran as a fluid-phase marker. FITC-dextran added to the medium accumulated rapidly inside the cells with a rate of influx equivalent to 9 microns3 of fluid/cell x min. After a period of about 90 min of uptake, the intracellular FITC-dextran level reached a plateau which corresponded to a strict balance between pinocytosis and exocytosis as shown both by efflux measurements and pulse experiments with (3H) dextran. At equilibrium, the amount of internalized marker reached a value equivalent to 790 microns3 of fluid taken up per amoeba, i.e. a volume paradoxically higher than the total aqueous space of the cell (520 microns3 ). FITC-dextran was thus markedly concentrated intracellularly. The endocytic compartment in which the intracellular FITC-dextran was concentrated could be completely washed out when FITC-dextran was removed from the external medium.
D003911:Dextrans; D004023:Dictyostelium / Q000166:cytology / Q000502:physiology*; D004705:Endocytosis; D005089:Exocytosis; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives*; D005452:Fluoresceins; D007700:Kinetics; D010873:Pinocytosis; D013395:Sucrose; D013997:Time Factors
D003911:Dextrans; D005452:Fluoresceins; C015219:fluorescein isothiocyanate dextran; D013395:Sucrose; D016650:Fluorescein-5-isothiocyanate