Renal transport of neutral amino acids. Tubular localization of Na+-dependent phenylalanine- and glucose-transport systems.
The transport properties for phenylalanine and glucose in luminal-membrane vesicles from outer cortex (pars convoluta) and outer medulla (pars recta) of rabbit kidney were studied by a spectrophotometric method. Uptake of phenylalanine as well as of glucose by the two types of membrane vesicles was found to be Na+-dependent, electrogenic and stereospecific. Na+-dependent transport of L-phenylalanine by outer-cortical membrane vesicles could be accounted for by one transport system (KA congruent to 1.5 mM). By contrast, in the outer-medullary preparation, L-phenylalanine transport occurred via two transport systems, namely a high-affinity system with K1A congruent to 0.33 mM and a low-affinity system with K2A congruent to 7 mM respectively. Na+-dependent uptake of D-glucose by pars convoluta and pars recta membrane vesicles could be described by single, but different, transport systems, namely a low-affinity system with KA congruent to 3.5 mM and a high-affinity system with KA congruent to 0.30 mM respectively. Attempts to calculate the stoichiometry of the different Na+/D-glucose transport systems by using Hill-type plots revealed that the ratio of the Na+/hexose co-transport probably is 1:1 in the case of pars convoluta and 2:1 in membrane vesicles from pars recta. The Na+/L-phenylalanine stoichiometry of the pars convoluta transporter probably is 1:1. Both the high-affinity and the low-affinity Na+-dependent L-phenylalanine transport system of pars recta membrane vesicles seem to operate with a 1:1 stoichiometry. The physiological importance of the arrangement of low-affinity and high-affinity transport systems along the kidney proximal tubule is discussed.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008854:Microscopy, Electron; D010649:Phenylalanine / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology*
D010649:Phenylalanine; D012964:Sodium; D005947:Glucose