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A choline transporter in renal brush-border membrane vesicles: energetics and structural specificity
S H Wright1, T M Wunz, T P Wunz
1Department of Physiology, College of Medicine, University of Arizona, Tucson 85724.
The Journal of Membrane Biology
|February 1, 1992
Summary
Renal reabsorption of choline is primarily mediated by a high-affinity electrogenic transporter, distinct from the organic cation/H+ exchanger. This pathway ensures efficient choline uptake in the kidney.
Area of Science:
- Nephrology
- Renal Physiology
- Molecular Transport
Background:
- Choline, a vital quaternary ammonium compound, is reabsorbed by renal proximal tubules.
- Its role as a substrate for the organic cation (OC) secretory pathway is known, but the reabsorption mechanism is unclear.
Purpose of the Study:
- To investigate the transport mechanisms responsible for renal choline reabsorption.
- To differentiate choline transport from the known renal organic cation (OC)/H+ exchanger.
Main Methods:
- Utilized rabbit renal brush-border membrane vesicles (BBMV) to study choline and tetraethylammonium (TEA) transport.
- Assessed the effects of H+ gradients, trans-substrate gradients, and electrical potential differences (PD) on uptake kinetics.
Main Results:
- Choline uptake was not stimulated by an outward H+ gradient, unlike TEA.
- A high-affinity transporter (Kt ~97 µM) with high specificity for choline was identified.
- An inside-negative electrical PD stimulated choline uptake, supporting an electrogenic pathway.
Conclusions:
- An electrogenic, high-affinity pathway is the primary mechanism for renal choline reabsorption.
- This pathway is distinct from the renal organic cation (OC)/H+ exchanger.
- Identified molecular determinants of substrate-transporter interactions for choline.