Membrane recycling: vesiculation of the amoeba contractile vacuole at systole.

Ultrastructural data on the protozoan Amoeba proteus support a model of membrane recycling. At systole the amoeba contractile vacuole fuses with the cell surface and expels its contents. Observations by electron microscopy indicate that, as the vacuole empties, its bounding membrane transforms into tiny (35 nanometers in diameter) vesicles, identical to the vesicles that segregate fluid and contribute to the diastolic vacuole.