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Na+ transport by brush border membrane from rat kidney
Biochemical and Biophysical Research Communications
|September 17, 1984
Summary
Rat kidney brush border membranes show high sodium (Na+) permeability. A Na+-H+ antiport system was identified, but overall Na+ uptake suggests leaky membranes compared to in vivo conditions.
Area of Science:
- Nephrology
- Renal Physiology
- Membrane Transport
Background:
- The kidney's brush border membrane plays a crucial role in ion reabsorption.
- Understanding sodium (Na+) transport mechanisms is vital for renal function.
- Previous studies suggested specific transporters, but membrane permeability remained unclear.
Purpose of the Study:
- To quantify Na+ uptake kinetics in rat renal brush border membrane vesicles.
- To identify the transporters involved in Na+ transport.
- To assess the passive permeability of the brush border membrane to Na+.
Main Methods:
- Isolation of brush border membrane vesicles from rat kidney cortex.
- Measurement of Na+ uptake under varying NaCl concentrations and pH gradients.
- Inhibition studies using amiloride.
- Analysis of uptake kinetics to determine diffusion and saturable components.
Main Results:
- Na+ uptake exhibited both diffusion and saturable components (Kt = 5 mM, Jmax = 0.62 pmol/microgram prot/s).
- Amiloride significantly inhibited Na+ uptake at 1 mM NaCl, and pH gradients stimulated uptake, indicating Na+-H+ antiport activity.
- Anion effects on Na+ uptake at high NaCl concentrations aligned with their known permeabilities, suggesting electrical potential generation.
Conclusions:
- Rat renal brush border membrane vesicles demonstrate significant leakiness to Na+.
- The identified Na+-H+ antiport is functional, but passive Na+ permeability is higher than anticipated in vivo.
- These findings necessitate a re-evaluation of Na+ handling in the renal brush border membrane.