The Plasma Membrane Potential and the Organization of the Actin Cytoskeleton of Epithelial Cells
Schemes showing some ionic transport systems of the plasma membrane. (a) In symmetric, nonpolarized cells the sodium pump maintains the electrochemical gradients of sodium and potassium across the plasma membrane. The sodium and potassium channels underlie the generation of a diffusion potential across the plasma membrane. Chloride is usually maintained at activities close to equilibrium. (b) In polarized epithelial cells the asymmetric distribution of, mainly, sodium channels and the sodium pump into distinctive apical and basolateral membranes may determine a net transcellular transport of sodium chloride. (ap: apical; bl: basolateral; the orange circles represent the sodium pump, and the other arrows correspond to ionic channels).
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