Summary: A study has been made of the uptake of radioactively-labelled solutes by starved myxamoebae of the cellular slime mould Inulin uptake was energy-dependent, inhibited by cycloheximide, and the rate was proportional to extracellular inulin concentration. The ability of the cells to take up inulin did not change during starvation. Uptake of four other solutes, β-alanine, glucose, protein hydrolysate and uracil occurred at a similar rate to inulin uptake when expressed as an endocytic index (μl medium taken up h per 10 cells). All the results were consistent with uptake occurring by fluid-phase pinocytosis. Pinocytic activity thus occurred in starving cells and was found to be affected by some agents that act as developmental inhibitors. Uptake of inulin and putrescine (previously shown to be taken up by adsorptive pinocytosis) was inhibited by chloroquine, KCl and NHCl, although ammonium ions also blocked developmental changes in the ability of myxamoebae to take up putrescine. Sodium ions were less inhibitory. ε-Aminocaproic acid inhibited solute uptake in a temperature-dependent, reversible manner.


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