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Citrate transport in proximal cell line
D Law1, K S Hering-Smith, L L Hamm
1Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
The American Journal of Physiology
|July 1, 1992
Summary
Opossum kidney (OK) cells reveal a novel sodium-dependent citrate transport process. This pathway differs from apical transporters and may involve trivalent citrate species, potentially representing basolateral membrane transport.
Area of Science:
- Nephrology
- Cell Biology
- Biochemistry
Background:
- Kidney proximal tubules handle citrate via apical and basolateral transporters.
- The basolateral citrate transport mechanism remains poorly understood.
Purpose of the Study:
- To investigate citrate transport in proximal tubule-like cells using the OK cell line.
- To characterize the properties of this novel citrate transport process.
Main Methods:
- Utilized [14C]citrate and [3H]mannitol for uptake studies in OK cell monolayers.
- Assessed sodium dependence, substrate concentration effects, and pH influence on citrate transport.
- Examined competitive inhibition by various di- and tricarboxylates.
Main Results:
- Citrate uptake was sodium-dependent and saturable.
- Transport showed minimal change from pH 6.2-7.0, increasing at pH 7.4-7.8.
- Dicarboxylates (except alpha-ketoglutarate) had minimal effect, while tricarboxylates significantly inhibited uptake.
- Mitochondrial tricarboxylate transporter inhibitor had no effect.
Conclusions:
- OK cells exhibit a novel citrate transport process distinct from apical transporters.
- This process likely involves the trivalent citrate species, unlike typical divalent transport.
- The identified transport may represent the basolateral membrane mechanism in proximal tubules.