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External solution driving forces for isotonic fluid absorption in proximal tubules
Federation Proceedings
|February 1, 1979
Summary
Lateral intercellular spaces in the mammalian proximal nephron do not drive volume absorption. Instead, osmotic gradients from anion differences or luminal hypotonicity are the primary forces, with anion differences being most significant.
Area of Science:
- Nephrology
- Renal Physiology
- Cell Biology
Background:
- The role of lateral intercellular spaces in proximal nephron volume absorption is debated.
- Low transepithelial resistance suggests these spaces may not act as a hypertonic compartment.
Purpose of the Study:
- To investigate the driving forces for volume absorption in the mammalian proximal nephron.
- To determine if lateral intercellular spaces function as a central compartment for volume absorption.
Main Methods:
- Assessed passive ion permeation via paracellular routes.
- Calculated hydraulic conductances of isolated convoluted and straight proximal tubules.
- Evaluated osmotic volume flow dependence on perfusion rate.
Main Results:
- Lateral intercellular spaces have insufficient diffusion resistance to create significant compositional differences.
- Proximal tubule segments exhibit high hydraulic conductances (3,000-5,000 micron/sec).
- Asymmetrical anion concentration differences and luminal hypotonicity were identified as driving forces for volume absorption.
Conclusions:
- Lateral intercellular spaces do not serve as a hypertonic compartment driving volume absorption.
- Osmotic gradients, particularly asymmetrical anion differences, are sufficient to explain proximal nephron volume absorption.
- Preferential HCO-3 reabsorption creating anion gradients is the quantitatively most important driving force.