Function of Tight Junctions
Tight junctions are thought to prevent interaction between lipid and proteins laterally across the two domains of the membrane. It is also a barrier to prevent certain molecules from leaving the basolateral side or entering via the apical side of the cells.
There have been several studies which have provided evidence that there is interaction of the two domains in the absence of tight junctions. For example, sphingomyelin, which is lipophilic, is labelled with bodipy and inserted into the apical membrane of the epithelial cell. In the presence of the tight junctions the sphingomyelin will remain in the apical membrane and not interact with the basolateral surfaces. However, if the tight junctions are disrupted then the sphingomyelin is seen to move to the basolateral membranes thus suggesting that the tight junctions are the reason for the maintanance of the cells polarity. These results are analysed using confocal imaging.