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Published on: September 12, 2015
Permeability changes in Necturus proximal tubule during volume expansion
The American Journal of Physiology
|March 1, 1978
Summary
Extracellular volume expansion in Necturus proximal tubules alters permeability. Increased tight junction permeability affects osmotic flow, while intercellular spaces regulate diffusional permeability for nonelectrolytes.
Area of Science:
- Nephrology
- Renal Physiology
- Cell Biology
Background:
- The proximal tubule plays a crucial role in reabsorption and maintaining fluid balance.
- Understanding epithelial permeability is vital for comprehending kidney function and fluid transport.
Purpose of the Study:
- To investigate the impact of extracellular volume expansion on Necturus proximal tubule permeability to hydrophilic nonelectrolytes.
- To differentiate the effects of volume expansion on osmotic and diffusional permeability.
Main Methods:
- Perfusion of Necturus proximal tubular segments under controlled conditions with zero net water flux.
- Measurement of transepithelial permeability to various nonelectrolytes (urea, mannitol, sucrose) and osmotic flow parameters.
- Analysis of reflection coefficients for nonelectrolytes at the apical surface.
Main Results:
- Volume expansion slightly increased urea permeability but decreased mannitol and significantly decreased sucrose permeability.
- The NaCl reflection coefficient decreased significantly in both summer and winter animals.
- Osmotic water flux and hydraulic conductivity increased in the lumen-to-capillary direction.
- Apical reflection coefficients for nonelectrolytes >3 Å radius decreased, suggesting distinct pore populations.
Conclusions:
- Volume expansion modifies Necturus proximal tubule permeability, impacting both osmotic and diffusional transport.
- Increased tight junction permeability likely accounts for altered osmotic flow parameters.
- The intercellular space is proposed as the primary regulator of diffusional permeability.
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