Na⁺-dependent hexose transport in vesicles from cultured renal epithelial cell line

Apical membrane vesicles were prepared from cultured epithelia formed by LLC-PK₁ cells using a calcium precipitation technique. α-Methylglucoside uptake into this vesicle preparation was markedly stimulated by sodium and inhibited by phlorizin. In addition, a transient 'overshoot' of intravesicular α-methylglucoside concentration above its equilibrium value was observed under initial sodium gradient conditions. The specificity of this sodium-dependent hexose transporter closely resembled that found in the mammalian kidney brush border membrane, e.g., α-methylglucoside, D-glucose, and D-galactose apparently share the transporter while 2-deoxy-D-glucose, mannose, and fructose do not. Kinetic analysis of the sodium-dependent component of α-methylglucoside flux into LLC-PK₁ apical membrane vesicles indicates the existence of single transporter with K(m) ≃ 2mM and V(max) ≃ 3 nmol.min^-1.mg protein^-1. Measurement of α-methylglucoside uptake as a function of sodium concentration is consistent with a sodium:sugar stoichiometry of approximately 2:1. There is a good correlation over time between the development of the concentrating capacity of the intact epithelium for α-methylglucoside and the transport properties of the vesicle preparation.