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Cytochalasin B is a drug that attaches to the barbed end of F-actin
and inhibits F-actin growth. This drug has several effects on
Paramecium, e.g., it inhibits digestive vacuole release and it
prevents the retrieval of spent vacuole membrane from the cytoproct
resulting in open cytoprocts. In thin sections large clumps of
amorphous material appear around the DV-I and these clumps are covered
by a layer of discoidal vesicles. Presumably membrane receptors that
bind actin to the DV-I membrane are present in the discoidal vesicles
and these receptors will bind to G-actin or partially polymerized
F-actin even without its complete polymerization into normal F-actin
filaments. However, without normal F-actin association with discoidal
vesicle-derived DV-I membrane the phagosome will not be removed in a
timely fashion from the cytopharynx and the acidosomes will be slow to
fuse, if they fuse at all, with the DV-I so that only 10% of the
vacuoles that do form will become acid and these will only become
mildly acid (~6.0 pH instead of ~3.0 pH as in vacuoles of control
cells; see Allen and Fok, J. Cell Biol. 97:566-570, 1983). EM taken on
10/14/81 by R. Allen with Hitachi HU11A TEM. Neg. 10,000X. Bar =
0.5µm. Published in Eur. J. Cell Biol. 37:35-43, 1985.
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