Polarity of Cell Membranes

Publisher Summary Many cells exhibit asymmetry or polarity. This polarity can be in the form of various membrane domains with distinct properties, asymmetric distribution of intracellular materials, polarized divisions of cells leading to distinct daughter cells, or polarity of cell structure. Such polarity is called spatial polarity. Cells can also exhibit temporal polarity, with marked changes arising during development or differentiation. This chapter explores that the best examples of polarized cells are epithelial cells, which have distinct apical membrane and basolateral membrane domains that differ in their lipid and protein compositions. This polarity of the transport proteins in epithelial cells is essential for the vectorial transport of solute and water across these cells. Neurons are another good example of polarized cells, with distinct dendritic, cell body, and axon regions. The axonal membrane of neurons is analogous to the apical membrane of epithelia, whereas the somatodendritic membrane is analogous to the basolateral membrane. Cell polarity can also be modified. For example, under conditions of ischemia, renal proximal tubule epithelial cells lose their polarity. By contrast, the polarity of chick embryo epiblast epithelial cells is switched to the opposite polarity by reversing the polarity of the transepithelial potential.