pH gradient-stimulated sulfate transport by rabbit ileal brush-border membrane vesicles: evidence for SO4-OH exchange

Am J Physiol. 1985 Nov;249(5 Pt 1):G607-13. doi: 10.1152/ajpgi.1985.249.5.G607.

Abstract

In the presence of a pH gradient (7.7 inside, 5.5 outside), the initial velocity of SO4 uptake by rabbit ileal brush-border membrane (BBM) vesicles was markedly stimulated compared with uptake in the absence of a pH gradient. Under pH gradient conditions, SO4 was transiently accumulated at a concentration 13-fold higher than at equilibrium ("overshoot"). Superimposition of a HCO3 gradient did not further stimulate the initial velocity of SO4 uptake compared with a pH gradient alone. Evidence that this pH gradient-stimulated SO4 uptake represented SO4-OH exchange included lack of sensitivity of SO4 transport to alterations of the membrane potential; 85-95% inhibition of SO4 uptake by the anion exchange inhibitors DIDS and SITS; and saturation kinetics (Km for SO4 = 0.475 +/- 0.054 mM; Vmax = 4.1 +/- 0.1 nmol SO4 X mg prot-1 X min-1). Sulfate did not inhibit pH gradient-stimulated 36Cl uptake, indicating that SO4-OH and Cl-HCO3(OH) are different exchangers. When BBM vesicles were compared with basolateral membrane (BLM) vesicles, pH gradient-stimulated SO4 uptake was found predominantly in the BBM preparation. Brush-border SO4-OH exchange was further localized by demonstrating Na-stimulated SO4 efflux from vesicles loaded under pH gradient conditions, suggesting that Na-SO4 cotransport and SO4-OH exchange are on the same BBM vesicles. In conclusion, a SO4-OH exchanger (or H-SO4 cotransporter) exists on the brush border of rabbit ileum which is distinct from the brush-border Cl-HCO3(OH) exchanger.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport
  • Chlorides / metabolism
  • Hydrogen-Ion Concentration
  • Hydroxides / metabolism*
  • Ileum / metabolism*
  • In Vitro Techniques
  • Ion Exchange / drug effects
  • Kinetics
  • Male
  • Microvilli / metabolism
  • Rabbits
  • Stimulation, Chemical
  • Sulfates / metabolism*
  • Tissue Distribution

Substances

  • Chlorides
  • Hydroxides
  • Sulfates