Abstract
The numerical densities of free and attached vesicles have been determined in the peripheral zone of canine arterial endothelium with the use of ruthenium red as an extracellular marker. Ruthenium red only penetrates pinocytotic invaginations that are continuous with the extracellular space, allowing the distinction of truly free vesicles from apparently free vesicles which are actually attached to the plasma membrane in a different section plane. Attached vesicles are distributed bimodally, with density maxima 20–40 nm from the luminal and abluminal cell membranes. Free vesicles show a nearly uniform distribution across the cytoplasm. Approximately three-fourths of the apparently free vesicles are attached, and only one-fourth of these are actually free. The ratio of attached vesicles to free vesicles obtained with the use of the ruthenium red is 11.29 ± 0.63 (mean ± SD). This ratio tended to be underestimated in studies in which an extracellular marker was not employed. These data on vesicle distribution are valuable in understanding the dynamics of vesicle attachment and for predicting the possible effects of enhanced vesicle diffusion on macromolecular transport.
Published Version
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