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Phosphate transport by rat intestinal basolateral-membrane vesicles
F K Ghishan1, K Kikuchi, N Arab
1Vanderbilt University Medical Center, Department of Pediatrics, Nashville, TN 37232.
The Biochemical Journal
|May 1, 1987
Summary
This study identifies a sodium-dependent phosphate carrier at the rat intestinal basolateral membrane. This carrier exhibits Michaelis-Menten kinetics and a 2 Na+:1 phosphate stoichiometry, crucial for phosphate absorption.
Area of Science:
- Physiology
- Molecular Biology
- Biochemistry
Background:
- Phosphate absorption is vital for maintaining mineral homeostasis.
- The specific mechanisms of phosphate transport at the intestinal basolateral membrane remain incompletely understood.
Purpose of the Study:
- To characterize the kinetic and mechanistic properties of phosphate transport across the rat intestinal basolateral membrane.
- To identify the presence and stoichiometry of a sodium-phosphate (Na+-Pi) cotransporter at this membrane.
Main Methods:
- Utilized enriched basolateral membrane preparations from rat intestine.
- Investigated phosphate transport kinetics using saturable, Na+-dependent uptake assays.
- Employed tracer-exchange and counter-transport studies to confirm carrier presence.
- Determined transporter stoichiometry using the static-head method at pH 7.4.
Main Results:
- Phosphate transport was saturable, Na+-dependent, and followed Michaelis-Menten kinetics (Vmax: 51.1 ± 4.2 pmol/10 s/mg protein, Km: 14 ± 3.9 µM).
- The transport process was electroneutral, with Na+ dependence attributed to a specific Na+-Pi carrier.
- Stoichiometry was determined to be 2 Na+:1 phosphate at pH 7.4.
- Confirmed the presence of a Na+-Pi carrier at the basolateral membrane.
Conclusions:
- This study provides the first direct evidence for a specific phosphate carrier at the intestinal basolateral membrane.
- The identified Na+-Pi cotransporter plays a significant role in regulating phosphate efflux from intestinal cells into the bloodstream.