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Phosphate transport in human jejunal brush-border membrane vesicles
1Department of Pediatric Gastroenterology, University of Virginia Medical Center, Charlottesville.
Gastroenterology
|January 1, 1989
Summary
Phosphate absorption in the human jejunum involves both passive diffusion and sodium-dependent transport, with higher rates observed at acidic pH. This suggests pH influences phosphate uptake mechanisms and ion cotransport.
Area of Science:
- Gastroenterology
- Renal Physiology
- Molecular Biology
Background:
- Phosphate is essential for numerous physiological processes.
- Intestinal phosphate absorption is crucial for maintaining phosphate homeostasis.
- The mechanisms of phosphate transport across the jejunal brush border are not fully elucidated.
Purpose of the Study:
- To investigate the characteristics of phosphate transport in human jejunal brush-border membrane vesicles.
- To determine the influence of pH on phosphate uptake kinetics and mechanisms.
- To elucidate the role of sodium cotransport in phosphate absorption.
Main Methods:
- Preparation of isolated brush-border membrane vesicles from human jejunum.
- Measurement of phosphate uptake at different pH values (6.1 and 7.4) and sodium concentrations.
- Kinetic analysis of carrier-mediated transport (Km, Vmax) and passive diffusion.
- Determination of transport charge (electroneutral vs. electrogenic).
Main Results:
- Phosphate transport exhibited two components: passive diffusion and sodium-dependent carrier-mediated uptake.
- Both transport components were significantly higher at pH 6.1 compared to pH 7.4.
- Sodium-dependent uptake was saturable, with a higher Vmax at pH 6.1, indicating pH-dependent carrier activity.
- Phosphate uptake was associated with the cotransport of two sodium ions, and the transport was electroneutral at pH 7.4 and electrogenic at pH 6.1.
Conclusions:
- Phosphate transport across the human jejunal brush border is influenced by pH.
- Both monovalent and divalent phosphate species are transported, with pH affecting the relative contributions of different transport mechanisms.
- The data suggest a pH-dependent shift in the electroneutrality of sodium-dependent phosphate cotransport.
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