Kinetic properties of galactose influx across the mucosal border of guinea pig ileum.

By using everted sac preparations of guinea pig ileum, properties of galactose influx across the mucosal border were studied under various ionic conditions of the media. Mannitol was used as a marker of the extracellular space on the mucosal surface. In the absence of Na+ in the mucosal medium, the "galactose space" was almost the same as mannitol space, indicating the lack of uptake of galactose through the specific carrier mechanism. Galactose influx obeyed Michaelis-Menten kinetics at any Na+ concentration and it was also a Michaelis-Menten type function of Na+ concentration in the medium when examined at a constant galactose concentration. The observed kinetic properties were well explained on the basis of the kinetic model in which galactose was assumed to be transported only in the form of galactose-Na-carrier complex. The increase in Na+ influx associated with galactose influx was not significantly different from galactose influx. Na+ concentration of the serosal medium had no effect on galactose influx across the mucosal border. Choline and Tris, as well as mannitol, had no stimulating or inhibitory effect on galactose influx.