Characteristics of intact lactose transport in rat jejunum in vitro.

The characteristics and kinetics of intact transmucosal transport of lactose have been studied in the rat jejunum using an everted sac preparation. Lactose transport displayed linear kinetics up to the maximum concentration (150 mM) of lactose studied. Ouabain (1 mM) when placed in the serosal solution, and phlorhizin (0.1 mM) when placed in the mucosal solution, had no significant effect on lactose transport. In contrast to glucose, transport of intact lactose did not occur against a concentration gradient. These results strongly suggest that intact transmucosal transport of lactose occurs by a process of simple passive diffusion, and that it is independent of the sodium-coupled glucose transport system.