Na+-dependent and Na+-independent betaine transport across the apical membrane of rat renal epithelium

Biochim Biophys Acta. 2015 Oct;1848(10 Pt A):2172-9. doi: 10.1016/j.bbamem.2015.05.020. Epub 2015 May 29.

Abstract

The low renal excretion of betaine indicates that the kidney efficiently reabsorbs the betaine filtered by the glomeruli but the mechanisms involved in such a process have been scarcely investigated. We have detected concentrative and non-concentrative betaine transport activity in brush-border membrane vesicles (BBMV) from rat renal cortex and medulla. The concentrative system is the Sodium/Imino-acid Transporter 1 (SIT1) because it is Na+- and Cl--dependent, electrogenic and is inhibited by an anti-SIT1 antibody. Its apparent affinity constant for betaine, Kt, is 1.1±0.5 mM and its maximal transport velocity, Vmax, 0.5±0.1 nmol betaine/mg protein/s. Inhibitors of the Na+/Cl-/betaine uptake are L-proline (75%) and cold betaine, L-carnitine and choline (40-60%). Neither creatine, TEA, taurine, β-alanine, GABA nor glycine significantly inhibited Na+/Cl-/betaine uptake. The non-concentrative betaine transport system is Na+- and H+-independent, electroneutral, with a Kt for betaine of 47±7 μM and a Vmax of 7.8±1 pmol betaine/mg protein/s. Its transport activity is nearly abolished by betaine, followed by L-carnitine (70-80%) and proline (40-50%), but a difference from the Na+/Cl-/betaine transport is that it is inhibited by TEA (approx. 50%) and unaffected by choline. The underlying carrier functions as an antiporter linking betaine entry into the BBMV with the efflux of either L-carnitine or betaine, an exchange unaffected by the anti-SIT1 antibody. As far as we know this is the first work reporting that betaine crosses the apical membrane of rat renal epithelium by SIT1 and by a Na+- and H+-independent transport system.

Keywords: Betaine; Brush-border membrane vesicles; Kidney; Transport.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Betaine / metabolism*
  • Biological Transport, Active
  • Cell Membrane / metabolism*
  • Cells, Cultured
  • Epithelial Cells / metabolism*
  • Kidney / metabolism*
  • Male
  • Metabolic Clearance Rate
  • Rats
  • Rats, Wistar
  • Sodium / metabolism*

Substances

  • Betaine
  • Sodium