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Endocytosis to digestive vacuoles. A summary of the movement of
extracellular ligands from the cell’s exterior to the digestive
vacuoles. Ligands are taken up in the parasomal sacs (clathrin-coated
pits) (CP) that pinch from the cell’s plasma membrane
(PM). Ligands labeled with antibodies (dots) enter the
pre-endosomal vesicles (PV) that soon lose their clathrin coats
and become part of the early endosome (EE) compartment by
fusion. Secondary coated pits form at the rims of these early endosome
cisternae and these also pinch off to form carrier vesicles
(CV) that still contain the ligands that have been released
from the receptors. The initial receptors are presumably recycled back
to the plasma membrane. The carrier vesicles lose their coats and bind
to the cytopharyngeal microtubular ribbons (CMR). They then
move along these ribbons toward the cytopharynx where they encounter
acidosomes (AC). They fuse with these acidosomes adding their
content and membrane to the acidosomes. When the acidosomes fuse with
the phagosome the ligands will enter the digestive vacuole system for
digestion and processing. Figure 3 in Allen and Peck, 1994, in K.
Hausmann and N. Hulpmann (eds.) Progress in Protozoology, pp 105-111,
Gustav Fischer Verlag, Stuttgart.
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