Kinetics of sugar transport in rabbit kidney cortex, In vitro: Movement of d-galactose, 2-deoxy- d-galactose and α-methyl- d-glucoside

Abstract

The kinetic parameters of d-galactose, 2-deoxy- d-galactose and α-methyl- d-glucoside transport were studied in rabbit kidney cortex slices. The following observations were made. 1. 1. A portion of the uphill transport of d-galactose does not require extra-cellular Na +. In the presence of external 118 mM Na + the maximal rate of d-galactose transport was increased 2.5-fold, the apparent K m of entry being unaffected. With regard to the Na + requirement, d-galactose transport appears to be intermediary between the practically Na +-independent uphill transport of 2-deoxy- d-galactose and the Na +-requiring uphill transport of α-methyl- d-glucoside. 2. 2. 2-Deoxy- d-galactose is an inhibitor of d-galactose transport (and vice-versa) both in the presence and in the absence of Na +. The respective K i' s are Na +-independent. 3. 3. The inhibition is of a partially competitive type, indicating that d-galactose and 2-deoxy- d-galactose share a common carrier with separate binding sites for each of the sugars. 4. 4. d-Galactose is a competitive inhibitor of α-methyl- d-glucoside transport. It may be concluded that the transport of the sugars examined by the kidney cortex cells is affected by a common carrier with several more or less independent binding sites, the Na + effect being more quantitative than qualitative in nature.