Cell volume regulation, alteration

Krane CM, Melvin JE, Nguyen HV, Richardson L, Towne JE, Doetschman T, Menon AG (2001) Salivary acinar cells from aquaporin 5-deficient mice have decreased membrane water permeability and altered cell volume regulation. J Biol Chem 276 23413-23420... 

Cell volume regulation can be altered as a result of direct membrane damage or from loss of metabolic energy. An aHeralion in eneigymetabolisfn can reduce die energy available to drive active transport and the synthesis cf macromolecules and to maintain osmotic balance. 

Although regulation of cell function by cell hydration has been studied most extensively in liver and renal cells, there is growing evidence that cell volume also determines cell function in other cell types. Moreover, alterations in cell hydration affect the volume of intracellular organelles, thereby modifying their function. For example, there is a close relationship between mitochondrial volume changes and mitochondrial function (see Halestrap, 1989,1993). 

Notably, all these characteristic alterations are conferred by cell membranes particularly the cytoplasmic membrane that is basically a lipid-bilayer structure imbedded with certain proteins. The lipid-bilayer forms a barrier to surround and protect the cell contents and the transmembrane proteins are responsible for the cell communications with the environment. For example, receptor proteins mediate the growth signals produced by growth factors and mitogens and any other stimuli. Ion channel proteins control the flux of ions across the cytoplasmic membrane to regulate membrane potential, osmolar-ity (or cell volume), etc. 

Whether or not the active transport of monovalent cations is rapidly increased by serum was not known when our investigation was started. There were reports of a several-fold increase in the activity of the Na+K+ ATPase after serum feeding and this is the enzyme responsible for the action of the sodium pump , which pumps out Na+ and pumps in K+. 13,i4> However, the ATPase measurements were made 24 hours after serum addition and we were interested in rapid responses. The question of serum effects on cation transport is important because the maintenance of an asymmetric distribution of K+ and Na+ ions has a profound influence in the regulation of cell functions such as cell volume,<45) transport of non-electrolytes,membrane potential,activity of glycolytic enzymes ) and macromolecular synthesis. 7) Thus, alteration in ionic pumping activity is another potential point of control in linking surface and intracellular events. 

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