Cell volume and ion transport regulation

Abstract

The cell membrane of virtually all animal cells is highly permeable to water, and hence cell volume is determined by the cellular content of osmotically active solutes, and by the osmolarity of the extracellular fluid. Maintenance of cell volume is thus a fundamental physiological process and a requirement for cell survival. In most animal cells total volume and water content are closely regulated (Gilles, 1978; Ma&night, 1988). Most animal cells defend themselves from colloid-osmotic swelling by the operation of ion pumps, which transport action ions from the intracellular to the extracellular compartment, therefore tending to reduce the intracellular concentration of permeant ions, and compensating for the excess concentration of impermeant solutes. This mechanism, referred to as the pumpleak hypothesis was first described by Wilson (1954) and then further proposed and substantiated by Leaf (1956) and Tosteson and Hoffman (1960). According to this hypothesis a constant cellular volume is achieved because the dominant extracellular diffusible cation, sodium, is effectively extruded from the cells through the activity of a sodium pump. The obligatory extracellular location of sodium effectively offsets the tendency for cells to swell as a consequence of the colloid osmotic force generated by the impermeant cell solutes. As originally proposed by Leaf (1956), the properties of