{'fraction_non_alphanumeric': 0.02909090909090909, 'fraction_numerical': 0.02181818181818182, 'mean_word_length': 5.589820359281437, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Endocytic activity of Sertoli cells grown in bicameral culture chambers

Immature rat Sertoli cells were cultured for 7 to 14 days on Millipore filters impregnated with a reconstituted basement membrane extract in dualenvironment (bicameral) culture chambers. Electron microscopy of the cultured cells revealed the presence of rod‐shaped mitochondria, Golgi apparatus, rough endoplasmic reticulum, and Sertoli‐Sertoli tight junctions, typical of these cells in vivo. The endocytic activity of both the apical and basal surfaces of the Sertoli cells was examined by either adding alpha2‐macroglobulin (alpha2‐M) conjugated to 20 nm gold particles to the apical chamber or by adding 125I labeled alpha2‐M to the basal chamber. During endocytosis from the apical surface of Sertoli cells, the alpha2‐M‐gold particles were bound initially to coated pits and then internalized into coated vesicles within 5 minutes. After 10 minutes, the alpha2‐M‐gold was found in multivesicular bodies (MVBs) and by 30 minutes it was present in the lysosomes. The proportion of alpha2‐M‐gold found within endocytic cell organelles after 1 hour of uptake was used to estimate the approximate time that this ligand spent in each type of organelle. The alpha2‐M‐gold was present in coated pits, coated vesicles, multivesicular bodies, and lysosomes for approximately 3, 11, 22, and 24 minutes, respectively. This indicates that the initial stages of endocytosis are rapid, whereas MVBs and lysosomes are relatively long‐lived. Since alpha2‐M‐gold was unable to permeate from the basal chamber through the Millipore filter to Sertoli cells, the uptake of alpha2‐M from the basal cytoplasm of Sertoli cells was studied using 125I‐alpha2‐M. After 2 hours incubation, approximately 1.7% of the added 125I‐alpha2‐M was taken up specifically by the basal cytoplasm of the Sertoli cells. Both alpha2‐M‐gold and 125I‐alpha2‐M could be displaced by increasing concentrations of unlabeled alpha2‐M. This indicates that alpha2‐macroglobulin was internalized by a receptor‐mediated endocytic process both from the apical surface and the basal surface of confluent epithelial sheets of Sertoli cells grown in bicameral culture chambers.