Journal of Cell Science, Vol 13, 677-686, Copyright © 1973 by Company of Biologists

Submitted on April 9, 1973

Cyclic Membrane Flow in the Ingestive-Digestive System of Peritrich Protozoans

II. Cup-Shaped Coated Vesicles

¹ Department of Anatomy, University of Wisconsin, Madison, WI. 53706, U.S.A.; Department of Anatomy, Upstate Medical Center, Syracuse, New York 13210, U.S.A.

As peritrich food vacuoles condense during the initial stage of digestion, excess membrane pinches off as cup-shaped vesicles which exhibit a structured coat on the non-cytoplasmic surface of the membrane. As the membrane cycles from cup-shaped vesicles to diskoidal vesicles to cytopharynx to food vacuoles, the coat undergoes structural transformations from the condensed form (5 x 16 nm peg-shaped elements) to an extended form (long thin filaments). Review of the literature reveals morphologically similar coats which undergo similar transformations in the digestive organelles of flagellate protozoa, Hydra absorptive cells, insect pericardial cells, ileal absorptive cells of suckling rats, cells of the guinea-pig placenta, mammalian Langerhans cells, and macrophages. The similar functional situation in which these coated membranes occur suggests that the coat is important to the recognition and binding of macromolecules.