Renal transport of neutral amino acids. Tubular localization of Na+-dependent phenylalanine- and glucose-transport systems

Abstract

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.

Glycylsarcosine uptake in rabbit renal brush border membrane vesicles isolated from outer cortex or outer medulla: Evidence for heterogeneous distribution of oligopeptide transporters

“…For BBMV isolated from rabbit outer medulla, ALP and Na + /K + -ATPase enrichment were 18.4 ± 2.7-fold and 1.4 ± 0.8-fold, respectively. These values were consistent with those reported previously (14)(15)(16) and demonstrate that the BBMV preparations were highly purified with negligible cross-contamination. To further validate the method of preparation for BBMVs (outer cortex vs. outer medulla), we examined the uptake of radiolabeled glucose in the presence of an inwardly directed sodium gradient (n = 7).…”

“…In this regard, outer cortical and outer medullary tissues were harvested separately from each kidney, as described previously (14)(15)(16). Typically, 6 kidneys were used for each preparation (about 2.2 g of tissue from outer cortex and 1.7 g from outer medulla).…”

Characterization of mouse amino acid transporter B0AT1 (slc6a19)

“…Closer inspection of reported K m values, however, reveals significant heterogeneity: for phenylalanine, for example, K m values between 1.5 mM and 10 mM were reported [2][3][4][5]; for leucine and valine, K m values were reported of 0.2 mM and 0.8 mM respectively [6]; and for alanine, K m values were found to vary between 0.4 and 8 mM [2,3,7]. Apart from the variability of the K m values, all studies agree in other properties of the system.…”

“…As a result, the transport activity is referred to as 'system B 0 ' to indicate its broad substrate specificity [9,10]. Despite the large variability of the reported K m values, it appears that the early segments of the proximal tubule (S1 and S2) most likely have only one transport activity for neutral amino acids, whereas two additional transport activities can be found in the S3 segment [4,6,11]. One of these activities has a higher affinity than that in the proximal tubule; the other has a lower affinity.…”

GTP‐binding proteins in luminal and basolateral membranes from pars convoluta and pars recta of rabbit kidney proximal tubule

“…10% of luminal membrane proteins. Previously we have demonstrated multiple aamino acid-No + co-transport systems in luminal membranes from pars convoluta or pars recta vesicles with different characteristics given by Vm,,~ and K~ [21][22][23][24][25][26][27]. Therefore, the preparation procedure was further examined by measuring several of these transport systems specific for the distinct regions of the proximal tubule.…”