Glycoprotein Synthesis of Renal Collecting Duct Epithelium Cultured as Globular Bodies

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Abstract
Cortical kidney explants from newborn New Zealand rabbits were cultured in Dulbecco’s minimum essential medium (DMEM) containing 10% fetal calf serum. Within 24 h the explants formed ‘globular bodies’ which were completely covered by a monolayered epithelium. The cells were differentiated and resembled collecting duct epithelium. By culturing the globular bodies in Dulbecco’s MEM with D-valine instead of L-valine, a monolayer of collecting duct cells was obtained and used for control experiments. For analysis and identification of synthesized glycoproteins, the globular bodies were incubated with various labelled carbohydrates and amino acids, and then fractionated. Glycoproteins secreted into the culture medium were not detected. Cell-associated glycoproteins were found in crude membrane fractions and then extracted with Triton X-100 for column chromatography, SDS-polyacrylamide electrophoresis in 6 M urea, isoelectrofocusing, and two-dimensional electrophoresis. Two prominent glycoproteins containing galactose and glucosamine were synthesized during the spreading of the epithelium, with an apparent molecular weight of 150,000 and 85,000 (SDS-PAGE). The synthesized glycoproteins differ in their content of radioactive glycoprotein precursor and leucine. The 85,000 dalton monomer glycoprotein has an isoelectric point of 3.5 and was identified by two-dimensional electrophoresis.