The mechanism of decreased Na +-dependent d-glucose transport in brush-border membrane vesicles from rabbit kidneys with experimental Fanconi syndrome

Abstract

In our previous paper (Yanase, M. et al. (1983) Biochim. Biophys. Acta 733, 95–101) we reported that the Na +-dependent d-glucose uptake into brush-border membrane vesicles is decreased in rabbits with experimental Fanconi syndrome (induced by anhydro-4-epitetracycline). In the present paper we investigate the mechanism underlying this decrease. d-Glucose is taken up into the osmotically active space in anhydro-4-epitetracycline-treated brush-border membrane vesicles and exhibits the same distribution volume and the same degree of nonspecific binding and trapping as in control brush-border membrane vesicles. The passive permeability properties of control and anhydro-4-epitetracycline-treated brush-border membrane vesicles are shown to be the same as measured by the time-dependence of l-glucose efflux from brush-border membrane vesicles. d-Glucose flux was measured by the equilibrium exchange procedure at constant external and internal Na + concentrations and zero potential. Kinetic analyses of Na +-dependent d-glucose flux indicate that V max in anhydro-4-epitetracycline-treated brush-border membrane vesicles (79.3 ± 7.6 nmol/min per mg protein) is significantly smaller than in control brush-border membrane vesicles (141.3 ± 9.9 nmol/min per mg protein), while the K m values in the two cases are not different from each other (22.3 ± 0.9 and 27.4 ± 1.8 nM, respectively). These results suggest that Na +-dependent d-glucose carriers per se are affected by anhydro-4-epitetracycline, and that this disorder is an important underlying mechanism in the decreased Na +-dependent d-glucose uptake into anhydro-4-epitetracycline-treated brush-border membrane vesicles.