Amino Acid Transport in Cultured Kidney Tubule Cells
Continuous cultures of epithelial cells that retain the ability to develop differentiated functions in vitro provide useful model systems in which to study the regulation of such functions. The LLC—PK1 line is one such cell line, which was derived from pig kidney by Hull and his co-workers in 1958 (Hull et al., 1976). It has been shown to have a near diploid chromosome number and does not produce tumors in immunosuppressed mice. When grown on a solid substratum, LLC—PK1 cells form monolayers that exhibit epithelial morphology: numerous microvilli are seen on the apical plasma membrane facing the culture medium, cells are connected by tight junctions near the apical surface, and beneath these the basolateral membrane foldings delineate a complex intercellular space (see, e.g., Fig. 1 in Misfeldt and Sanders, 1981). Unlike other epithelial cells, LLC—PK1 cells do not form permeable intercellular junctions as judged by their inability to transfer uridine nucleotides transcellularly (Sepúlveda and Pearson, 1984a). This correlates with the absence of gap junctions from electron microscope images of freeze-fractured monolayers (unpublished results from our laboratory). In addition to their general epithelial morphology, LLC—PK1 cells form domelike structures upon reaching confluency (Hull et al., 1976). These fluid-filled cavities are believed to arise from active transport of water across the cells into the space between the monolayer and the substratum (Abaza et al., 1974).
KeywordsBasolateral Membrane Amino Acid Transport Brush Border Membrane Neutral Amino Acid Brush Border Membrane Vesicle
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