In vivo , epithelial cells exhibit basolateral and apical surfaces. The tight ju
ID: 206398 • Letter: I
Question
In vivo, epithelial cells exhibit basolateral and apical surfaces. The tight junctional complex separates these two distinct cell surfaces from each other and joins the cells into an epithelial cell layer. In vivo cells showing such properties are resistant to ion flow across the cell layer. In vitro, many cultured epithelial cell systems show high electrical resistance but fail to exhibit a polarized distribution of proteins and lipids between the apical and basolateral surfaces. Present a working hypothesis to explain this outcome. In vivo, epithelial cells exhibit basolateral and apical surfaces. The tight junctional complex separates these two distinct cell surfaces from each other and joins the cells into an epithelial cell layer. In vivo cells showing such properties are resistant to ion flow across the cell layer. In vitro, many cultured epithelial cell systems show high electrical resistance but fail to exhibit a polarized distribution of proteins and lipids between the apical and basolateral surfaces. Present a working hypothesis to explain this outcome.Explanation / Answer
The epithelial cells form a barrier because cells are linked by tight junctions, which prevent many substances from diffusing between adjacent cells. For a subs tance to cross the epithelium, it must be transported across the cell membrane by membrane transporters Moreover, epithelial cells are able to transport substances in one direction across the epithelium because different sets of transporters are localised in either the apical or basolateral membranes.
The cell layers are morphologically polar . It has been found that miscelles are able to translocate across cell layers. The presence of inhibitors of endocytic process such as Nan3 and hypertonic sucrose attenuated the cellular uptake and traficking of miscelles. So, transport of substances across the epiyhelium in vitro is facilitated by clathrin- energy- and cholesterol mediated endocytosis.
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