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The passage of cytoplasmic vesicles across endothelial and mesothelial cells
Author(s) -
Smith J. R. Casley,
Chin J. C.
Publication year - 1971
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1971.tb02280.x
Subject(s) - vesicle , cytoplasm , biophysics , horseradish peroxidase , chemistry , ferritin , ferrocyanide , mesothelium , diffusion , membrane , biochemistry , biology , anatomy , physics , enzyme , electrode , peritoneum , thermodynamics
SUMMARY The proportions of labelled cytoplasmic vesicles, at increasing distances across mouse heart endothelium and diaphragmatic mesothelium, were studied using the following electron‐microscopical tracers: ferritin, horseradish peroxidase and sodium ferrocyanide. The cells were incubated in Hank's solution containing the tracer for periods of 2 sec up to 30 min. Peroxidase labelled the vesicles well, but ferrocyanide may have escaped from them into the cytoplasm. Both passed down the intercellular junctions. Ferritin showed evidence of molecular sieving when entering the vesicles, and probably also suffered from this on leaving them. It was possible to allow for these effects. The vesicles containing tracers were found to have traversed the cells after only a few seconds; by approximately 10 sec a steady‐state was observed, after which there were constant proportions of labelled vesicles. These proportions decreased slightly, but not sharply, across the cells. It was found that the observed distributions across the cells were very similar to those predicted by diffusion theory, assuming the following postulates: (1) the vesicles are moved solely by Brownian motion; (2) a low (i.e. α = 0.05) probability that a collision with a plasma membrane results in fusion. If however it was assumed that the fusion probability (α) were unity, the observed distributions of labelled vesicles differed very significantly from those predicted. A possible explanation of the observed low value of α is suggested, based on mutually‐repelling charges on the vesicles and membranes. If α is given a value of around 0.05, the observations agree with calculated predictions that the median transit times for vesicles through cells 0.3–0.5 μm wide are approximately 3–5 sec and that the cytoplasmic viscosity is approximately 0.2–0.3 poise. The predictions of vesicular median free lives of‐ sec and median attachment times of 3–5 sec also received confirmation, as did the prediction that some 40% of the released vesicles regain the membrane on the opposite side of the cell.