Observations on endocytosis in tissue culture
Date
1972
Authors
Becker, Gregory Mark
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Abstract
Endocytosis in Chinese hamster ovary fibroblasts was investigated by measuring the rate of uptake of sucrose-³H, which is known to enter cells only by endocytosis. Serum, polyvinylpyrrolidone (PVP), adenosine triphosphate, insulin, and cyclic adenosine monophosphate, all of which are known to increase the rate of endocytosis by other cell systems, had no effect on Chinese hamster fibroblasts. However, medium in which these cells had been maintained for several days, referred to as conditioned medium, had a profound effect on endocytosis. These cells endocytosed 3 to 5 times as rapidly in conditioned medium as in fresh medium. A logarithmic inhibition of this effect was observed with increasing concentrations of D-glucose, however glucose free medium did not produce as great an effect as conditioned medium. This suggests that these cells
may endocytose in response to their nutritional requirements.
Cytochalasin B, which is known to cause disruption of microfilaments, suppressed, but did not completely inhibit endccyto3is by Chinese hamster fibroblasts. Cells derived from a benign human prostatic hypertrophy were effected similarly. This suggests both the involvement of microfilaments in endocytosis, and the possibility that there exists in these cells microfilaments which are relatively insensitive to the effects of cytochalasin B.
High resolution morphological studies on the effect of cytochalasin B showed that membrane ruffling, thought to be essential for endocytosis, is completely suppressed by cytochalasin B.
Morphological observations on the effect of the endocytosis of the polymers dextran and PVP by both the hamster and human prostatic cell lines demonstrated the profound effects these polymers can have on secondary lysosomes. In particular PVP was found to have a very marked deleterious effect on the human prostatic cell line, which presumably is a result of a disruption of the lysosomal-vacuolar system of these cells.
Insulin, 17-β-estradiol and testosterone were shown to have no effect on endocytosis by the hamster cell line, however insulin induced membrane ruffling with these cells, without however, a concomitant increase in endocytosis.
No correlation was observed between the endocytosis of the polymers dextran and PVP and the cryoprotective action these polymers exhibit with the hamster cell line. These polymers were also shown not to bind to the plasma membrane of these cells, indicating that their cryoprotective action is not related to either their intracellular presence or to binding to the plasma membrane of these cells.