Characteristics of D-galactose transport systems by luminal membrane vesicles from rabbit kidney

• Published in: Biochimica et biophysica acta Vol. 856; no. 3; pp. 578 - 584
• Main Authors: Røigaard-Petersen, H, Jacobsen, C, Sheikh, M I
• Format: Journal Article
• Language: English
• Published: Netherlands 25.04.1986
• Subjects: Animals; Biological Transport; Cell Membrane - metabolism; Cerebral Cortex - metabolism; Galactose - metabolism; Glucose - metabolism; In Vitro Techniques; Kidney Tubules - metabolism; Kinetics; Monosaccharide Transport Proteins - analysis; Potassium - metabolism; Rabbits; Sodium - metabolism; Structure-Activity Relationship
• ISSN: 0006-3002
• DOI: 10.1016/0005-2736(86)90150-1

The characteristics of renal transport of D-galactose by luminal membrane vesicles from either whole cortex, pars recta or pars convoluta of rabbit proximal tubule were investigated by a spectrophotometric method using a potential-sensitive carbocyanine dye. Uptake of D-galactose by luminal membrane vesicles prepared from whole cortex was carried out by an Na+-dependent and electrogenic process. Eadie-Hofstee analysis of saturation-kinetic data suggested the presence of multiple transport systems in vesicles from whole cortex for the uptake of D-galactose. Tubular localization of the transport systems was studied by the use of vesicles derived from pars recta and pars convoluta. In pars recta, Na+-dependent transport of D-galactose and D-glucose occurred by means of a high-affinity system (half-saturation: D-galactose, 0.15 +/- 0.02 mM; D-glucose, 0.13 +/- 0.02 mM). These results indicated that the "carrier' responsible for the uptake of these hexoses does not discriminate between the steric position of the C-4 hydroxyl group of these two isomers. This is further confirmed by competition experiments, which showed that D-galactose and D-glucose are taken up by the same and equal affinity transport system by these vesicle preparations. Uptake of D-galactose and D-glucose by luminal membrane vesicles isolated from pars convoluta was mediated by a low-affinity common transport system (half-saturation: D-galactose, 15 +/- 2 mM; D-glucose, 2.5 +/- 0.5 mM). These findings strongly suggested that the "carrier' involved in the transport of monosaccharides in vesicles from pars convoluta is specific for the steric position of the C-4 hydroxyl group of these sugars and presumably interacts only with D-glucose at normal physiological concentration.