Abstract
UT-B1 is one of the isoforms of facilitated urea transporters that mediate rapid, passive movement of urea across cell membranes, and are candidates for regulators of urea permeability in the cell membrane. Our experimental results indicated the UT-B1 function as active water transporter against osmotic gradient in C6 glial cells. Exposure of C6 cells to a hyperosmotic (+ 300 mOsm/kg H2O) solution containing glycerol or sucrose produced cell shrinkage (about 20% decrease) due to water efflux according to osmotic gradient for water movement. On the other hand, C6 cells showed cell swelling (about 6% increase) against osmotic gradient for water movement just after exposure to a hyperosmotic solution containing urea, indicating that water influx against osmotic gradient for water movement is accelerated by urea; i.e., urea performs active water transport. Exposure of C6 cells to hypertonic urea media with a specific inhibitor for UT-B, pCMBS (500 μM), blocked the urea-induced swelling, but induced immediate, abrupt cell shrinkage (about 27% decrease). The urea-induced cell swelling was significantly suppressed in the siRNA-induced UT-B1-knockdown C6 cells. Taken together, these observations indicate that UT-B1 acts as an active water transporter and as a key molecule of water and urea excretion through the so-called astrocyte network. [J Physiol Sci. 2007;57 Suppl:S121]
