Evidence for the existence of a distinct SO4---OH- exchange mechanism in the human proximal colonic apical membrane vesicles and its possible role in chloride transport

Sangerta Tyagi, Reena J. Kavilaveettil, Waddah A. Alrefai, Shadwan Alsafwah, Krishnamurthy Ramaswamy, Pradeep K. Dudeja

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Abstract

Recent studies have demonstrated that mutations in human downregulated in adenoma gene (DRA) result in congenital chloride diarrhea (CLD), and that DRA may be involved in chloride transport across the intestinal apical domains. DRA is highly homologous to sulfate transporters, but not to any member of the anion exchanger gene family (AEs). Our previous studies have characterized the existence of a distinct Cl--OH- (HCO3-) exchanger, with minimal affinity for sulfate in the human colonic apical membrane vesicles (AMV). However, the mechanism(s) of sulfate movement across the colonocyte plasma membranes in the human colon is not well understood. Current studies were undertaken to elucidate sulfate transport pathways in AMVs of human proximal colon. Purified AMV and rapid filtration 35SO4-- uptake techniques were used. Our results demonstrate the presence of a pH gradient-driven carrier-mediated SO4---OH- exchange process in the human proximal colonic luminal membranes based on the following: a marked increase in the SO4-- uptake in the presence of an outwardly directed OH- gradient; a significant inhibition of SO4-- uptake by the membrane anion transport inhibitor, DIDS; demonstration of saturation kinetics (Km for SO4--: 0.80 ± 0.17 mM and Vmax 649 ± 74 pmol/mg protein/10 sec); competitive inhibition of SO4---OH- exchange by oxalate; SO4-- uptake was insensitive to alterations in the membrane potential; and inwardly directed Na+ gradient under non-pH gradient conditions did not stimulate SO4-- uptake. SO4-- uptake was significantly inhibited by increasing concentrations of chloride (1-10 mM) in the incubation media with a Ki for Cl- of 9.3 ± 1.4 mM. In contrast, OH-/HCO3- gradient-driven 36Cl- uptake into these vesicles was unaffected by increasing concentrations of sulfate (10-50 mM). The above data indicate that two distinct transporters may be involved in SO4-- and Cl- transport in the human intestinal apical membranes: an anion exchanger with high affinity for SO4-- and oxalate but low affinity for Cl-, and a distinct Cl--OH- (HCO3-) exchanger with low affinity for SO4--.

Original languageEnglish (US)
Pages (from-to)912-918
Number of pages7
JournalExperimental Biology and Medicine
Volume226
Issue number10
StatePublished - Nov 1 2001

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Chlorides
Sulfates
Membranes
Genes
Chloride-Bicarbonate Antiporters
Adenoma
Anions
Down-Regulation
Oxalates
Colon
4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid
Proton-Motive Force
Cell membranes
Membrane Potentials
hydroxide ion
Demonstrations
Cell Membrane
Mutation
Kinetics
Proteins

All Science Journal Classification (ASJC) codes

  • Biochemistry, Genetics and Molecular Biology(all)

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Evidence for the existence of a distinct SO4---OH- exchange mechanism in the human proximal colonic apical membrane vesicles and its possible role in chloride transport. / Tyagi, Sangerta; Kavilaveettil, Reena J.; Alrefai, Waddah A.; Alsafwah, Shadwan; Ramaswamy, Krishnamurthy; Dudeja, Pradeep K.

In: Experimental Biology and Medicine, Vol. 226, No. 10, 01.11.2001, p. 912-918.

Research output: Contribution to journalArticle

Tyagi, Sangerta ; Kavilaveettil, Reena J. ; Alrefai, Waddah A. ; Alsafwah, Shadwan ; Ramaswamy, Krishnamurthy ; Dudeja, Pradeep K. / Evidence for the existence of a distinct SO4---OH- exchange mechanism in the human proximal colonic apical membrane vesicles and its possible role in chloride transport. In: Experimental Biology and Medicine. 2001 ; Vol. 226, No. 10. pp. 912-918.
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