Sodium-coupled ion cotransport and the volume regulatory increase response.

In conclusion, maintenance of volume homeostasis is a fundamental requirement of all cells. For many cell types, this process requires expression of ion cotransport mechanisms as well as accumulation of osmotically-active organic compounds. Recent observations have indicated that the cellular mechanisms responsible for modulating hypertonic volume regulation are complex and appear to involve hormonal, biochemical and physico-chemical stimuli. Knowledge of the specific ion-transport mechanisms involved in the initial phase of VRI, the factors that control their expression, and the interrelationships between inorganic and organic solute accumulation will be required before an in depth understanding of hypertonic cell volume regulation in medullary nephron segments can be achieved.