Stoichiometry of organic anion/dicarboxylate exchange in membrane vesicles from rat renal cortex and hOAT1-expressing cells.
Although membrane vesicle studies have established the driving forces that mediate renal organic anion secretion and the organic anion transporter Oat1 has now been cloned in several species, its stoichiometry has remained uncertain. In this study, we used electrophysiology, kinetic measurements, and static head experiments to determine the coupling ratio for Oat1-mediated organic anion/dicarboxylate exchange. Initial experiments demonstrated that uptake of PAH by voltage-clamped Xenopus laevis oocytes expressing rOat1 led to net entry of positive charge, suggesting that coupling was one-to-one. This conclusion was confirmed by kinetic analysis of PAH and glutarate fluxes in native basolateral membrane vesicles from the rat renal cortex, which showed a Hill coefficient of 1. Similarly, static head experiments on the rat vesicles also showed a 1:1 coupling ratio. To confirm these conclusions in a system expressing a single cloned transporter, Madin-Darby canine kidney cells were stably transfected with the human exchanger hOAT1. The hOAT1-expressing cell line showed extensive PAH transport, which was very similar in all respects to transport expressed by hOAT1 in Xenopus oocytes. Its Km for PAH was 8 microM and glutarate effectively trans-stimulated PAH transport. When stoichiometry was assessed using plasma membranes isolated from the hOAT1-expressing cells, both kinetic and static head data indicated that hOAT1 also demonstrated a 1:1 coupling between organic anion and dicarboxylate.
Aslamkhan
Amy
A
Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Han
Yong-Hae
YH
Walden
Ramsey
R
Sweet
Douglas H
DH
Pritchard
John B
JB
D000818:Animals; D000838:Anions / Q000378:metabolism*; D002460:Cell Line; D055598:Chemical Phenomena; D002621:Chemistry; D003998:Dicarboxylic Acids / Q000378:metabolism*; D004285:Dogs; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008433:Mathematics; D009865:Oocytes / Q000502:physiology; D027362:Organic Anion Transport Protein 1 / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D014982:Xenopus laevis; D010130:p-Aminohippuric Acid / Q000493:pharmacokinetics
D000838:Anions; D003998:Dicarboxylic Acids; D027362:Organic Anion Transport Protein 1; D010130:p-Aminohippuric Acid