All cells must maintain a relatively constant volume in order to function properly. The PI will use fish to study cell volume regulation since they are excellent subjects in which to study this process. When marine fish move into brackish water from sea water they are confronted with a dilution of their body fluids because of the more dilute environment. To avoid a resultant swelling of their cells they unload ions and small organic molecules from their cells and thus balance the osmolarity (concentration of salts) between the inside and outside of their cells. A non-essential amino acid, taurine, is a prime component of this regulatory mechanism. Following dilution of the extracellular fluid taurine is released from the cells into the blood and must then be eliminated from the body. As it is not metabolised it must be excreted by the kidneys. The PI has shown that the marine fish secrete this compound across the kidney tubule cell by a transport system that is dependent on sodium ion and partially dependent on chloride ion. The mammalian kidney appears to have a similar transport system but it moves in the opposite direction; taurine is reabsorbed by the kidney. In this project the PI intends to further characterize this transport system and study its regulatory mechanisms. The information gained in these studies should increase understanding of how cells regulate their volume when confronted by changes in the concentration of the extracellular fluids.
