Premium
Human Organic‐Anion‐Transporter 4 facilitates unsymmetrical organic anion/OH‐ or Cl‐ exchange
Author(s) -
Hagos Yohannes,
Stein Daniel,
Ugele Bernhard,
Burckhardt Gerhard,
Bahn Andrew Bahn
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a340-b
Subject(s) - chemistry , probenecid , organic anion , organic anion transporter 1 , transporter , chloride , substrate (aquarium) , ion , biochemistry , endocrinology , organic chemistry , biology , gene , ecology
Human Organic‐Anion‐Transporter 4 is expressed in placenta, kidney and intestine. In the kidney it was localized on the apical side of proximal tubule cells facilitating the uptake of estrone sulphate and dehydroepiandrosterone‐sulphate. Generally, hOAT4 possesses a broad substrate spectrum. To date, the transport mode ‐ putative counter‐ions – of hOAT4 are still controversial. To address this question, we reevaluated the mode of action of this transporter. Transport studies using HEK293 cells stably transfected with hOAT4 showed a Km of 253 μM for 6‐carboxyfluorescein. Accumulation of 6‐CF and ES were inhibited by ES, DHEA‐S and probenecid, whereas p‐aminohippurate, lactate, pyrazinoate, glutarate exhibited no reduction of hOAT4 transport rate. Urate showed a significant inhibition of 6‐CF uptake and an IC50 value of 925 μM measured with ES. Trans‐stimulation studies revealed PAH and glutarate as potential exchange anions, elevating 6‐CF uptake, and documenting that hOAT4 works in an unsymmetrical mode. Urate and ES uptake were enhanced by chloride free medium, indicating chloride as one possible counter‐ion. This is further supported by an acidification of the external medium leading to a 6‐CF uptake by 3.5 fold and ES uptake by 1.6 fold consistent with the idea of an exchange of organic anions against, inorganic anions (Cl‐ or OH‐), most likely OH‐ ions under physiological conditions in the proximal tubule.