Archives   Cellular Transport and the Cell Cycle Posted April 1, 1998 Simple changes in a cell's volume can disrupt the proper functioning of living cells. For example, if a brain cell swells, the brain's function becomes impaired and serious consequences can occur. Yet, when any type of cell, including brain cells, takes in nutrients such as glucose or amino acids, it faces a challenge to homeostasis. The act of taking in nutrients could endanger the cell unless the cell restores proper osmotic balance. Because each cell constantly takes in nutrients and inorganic molecules such as ions, it is also constantly changing its osmotic balance. This leads to an influx of water and cell swelling. Because the cell swelling will disrupt the cell function, the cell needs a mechanism that will enable it to constantly maintain its correct volume. Recently scientists have shown that as a cell begins to accumulate nutrients, such as amino acids, a counterbalancing effect in the cell maintains homeostasis. How does this occur? When nutrients and water enter the cell, it moves positively-charged potassium and chloride ions to the outside of the cell. To accomplish this, the cell activates ion pumps in the plasma membrane. The expulsion of chloride ions is followed by an outflow of water, restoring proper cell volume and osmotic balance within the cell. Cells constantly maintain their shape and volume as they take in and metabolize nutrients and expel waste products. Each cell must maintain its unique shape and volume - whether it is a doughnut-shaped red blood cell or a cuboidal root tip cell. How does each kind of cell determine its unique shape? Scientists do not have the complete answer to this question yet, but it appears that cell shape also may involve the regulation of the same ion channels and pumps in the plasma membrane of the cell. References Lang, Florian and Siegfried Waldegger. "Regulating Cell Volume," American Scientist, Vol.85, Sept-Oct., 1997, pp. 456-463.