Pflügers Archiv

, Volume 418, Issue 4, pp 393–399 | Cite as

Transport of l-leucine hydroxy analogue and l-lactate in rabbit small-intestinal brush-border membrane vesicles

  • Manfred Friedrich
  • Heini Murer
  • Eric G. Berger
Transport Processes, Metabolism and Endocrinology; Kidney, Gastrointestinal Tract, and Exocrine Glands

Abstract

Substitution of the α-amino group of amino acids by hydroxyl groups yields hydroxy analogues (HA), which have been ascribed beneficial effects in nitrogensparing diets for uremic patients. In this study, intestinal uptake of l-leucine HA (l-LeuHA) and l-lactate into rabbit jejunal brush-border membrane vesicles was investigated. An inward-directed H+ or Na+ gradient stimulated uptake of both labelled substrates in a voltageclamped assay. The H+ gradient was the major driving force of uptake as compared with the Na+ gradient, and it led to a transient accumulation of both l-LeuHA and l-lactate. The proton ionophore carbonylcyanide p trifluoromethoxyphenylhydrazone (FCCP) reduced the initial H+-gradient-driven uptake rates of both substrates, but was without effect on Na+-gradient-driven uptakes. The H+-gradient-driven l-LeuHA uptake was saturable (apparent Kt = 15.4 mM). α-HA of l-leucine, l-isoleucine, l-valine, d-leucine, d-valine or l-lactate inhibited the H+-gradient-driven l-LeuHA or l-lactate uptakes whereas free branched-chain amino acids had no effect. Preloading the vesicles with one of the l-or d-HA of branched-chain amino acids or with l-lactate stimulated tracer l-LeuHA and also tracer l-lactate uptakes in the presence of a H+ gradient. It is concluded that H+-gradient-driven transport of l- and d-stereoisomeric HA of branched-chain amino acids as well as of l-lactate across rabbit intestinal brush-border membranes is mediated by the same carrier. Furthermore, there exists a Na+gradient-driven l-lactate transport system in the rabbit intestinal brush-border membrane.

Key words

Co-transport Nitrogen-sparing diet Proton-driven transport 

Terminology used

l-leucine hydroxy analogue l-2-hydroxy-4-methylpentanoic acid l-isoleucine hydroxy analogue l-2-hydroxy-3-methylpentanoic acid l-valine hydroxy analogue l-2-hydroxy-3-methylbutanoic acid l-lactate l-2-hydroxypropionic acid dl-methionine 2-hydroxy-4-methylthiobutanoic acid 

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Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Manfred Friedrich
    • 1
  • Heini Murer
    • 1
  • Eric G. Berger
    • 1
  1. 1.Institute of PhysiologyUniversity of ZürichZürichSwitzerland

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