PROGRESS IN PROTOZOOLOGY

276 H. PLATTNER ET AL»
(stretched and shot out) by exogenous Ca 2+ , once Ca 2+ can come in via
the already formed exocytotic canal (B i 1 i n s k i et al. 1981a).
Conclusions
Mebrane-integrated and membrane-associated proteins may exert
a modulating effect on membrane fusion in ciliates, other protozoa and
even in metazoan cells. At least some of these systems display conspicuous
ultrastructural details which could be interpreted along these
lines. The actual membrane fusion appears to be a focally restricted
event. In retrospect it appears now that research on membrane fusion
in protozoa has provided important clues for a general understanding of
membrane fusion processes. Such research appears also important with
regard to the interaction of protozoan parasites and host cells.
ACKNOWLEDGEMENTS
We thank Prof. J. Beisson for providing us generously some of her mutations,
for allowing us to reproduce the freeze-fracture micrographs of Fig. 3 and for giving
us valuable suggestions and criticism to this article. We also gratefully acknowledge
the skilful technical (assistance of Miss C. Braun, Mrs. R. Hildebramd and
Mrs. R. Sturzl as well as the secretarial help of Mrs. U. Remensperger. Supported
by SFB 138.
b
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