Regulation of expression of the sodium-coupled hexose transporter in cultured LLC-PK1 epithelia.

A variety of techniques have been used to study the sodium-coupled hexose transporter in epithelia formed by LLC-PK1 cells. The expression of the transporter is affected by the density and age of the culture and by the concentration of glucose in the growth medium. Sodium-coupled hexose transport appears as the epithelium becomes confluent and increases further as the epithelium matures. The increased transport is associated with increased transport in apical plasma membrane vesicles. Epithelia grown in medium containing 5 mM glucose express more transporters than epithelia grown in medium containing 25 mM glucose. The increase in transport is not the result of an extracellular signal that is generated as a consequence of the concentration of glucose. The response to different hexoses that are or are not transported on the carrier indicates that it is the metabolism of glucose that acts as the signal for expression of more or fewer transporters. The results are compared to similar studies of the effects of substrate concentration on expression of transporters in cultured fibroblasts and the intestines in situ.