Structural identification of brush border membrane transport systems ? towards an understanding of regulatory mechanisms

1993 ◽  
Vol 71 (10) ◽  
Author(s):  
H. Murer ◽  
J. Biber
Keyword(s):  
Membrane Transport ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Structural Identification ◽  
Regulatory Mechanisms ◽  
Transport Systems ◽  
Membrane Transport Systems

Transport characteristics of renal brush border Na(+)- and K(+)-dependent uridine carriers

1990 ◽  
Vol 258 (5) ◽  
pp. F1203-F1210 ◽  
Author(s):  
C. W. Lee ◽  
C. I. Cheeseman ◽  
S. M. Jarvis
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Positive Charge ◽  
Membrane Vesicles ◽  
Transport Processes ◽  
Transport Systems ◽  
Uridine Uptake ◽  
Renal Brush Border Membrane ◽  
Coupling Stoichiometry ◽  
Renal Brush Border

The uptake of uridine into rat renal brush-border membrane vesicles is mediated by Na(+)- and K(+)-dependent concentrative transport processes. At a 100 mM extravesicular cation concentration the apparent Km values were 9.7 +/- 4.2 and 28 +/- 5 microM, and Vmax values were 28 +/- 4 and 7 +/- 1 pmol.mg protein-1.s-1 for the Na(+)- and K(+)-dependent systems, respectively. Uracil, D-ribose, and D-glucose failed to inhibit the uptake processes, indicating that these carriers are specific for nucleosides. Other purines and pyrimidines inhibited uridine uptake competitively, although these two transport systems seem to favor adenosine and pyrimidines as permeants. Evidence is also given that transport is rheogenic, involving a net transfer of positive charge. The Na+:uridine and K+:uridine coupling stoichiometry was found to be 1:1 and 3:2, respectively. Both systems can also be driven by an anion gradient with apparent NO3- affinity (KNO3-) values of 42 +/- 13 and 163 +/- 54 mM for Na(+)- and K(+)-dependent systems, respectively.

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