Effective osmotic gradients have been postulated to exist between proximal tubule luminal fluid and its adjacent peritubular capillaries. The present studies were designed to examine this issue by measurement of the reflection coefficients of sodium chloride, sodium bicarbonate, glucose and alanine across the latter segments of both superficial and juxtamedullary proximal convoluted tubules. All studies were conducted by in vitro techniques using segments of rabbit nephrons in which net fluid efflux due to a raffinose concentration gradient was compared to fluid movement induced by equiosmolal gradients of test solute. The findings indicate that across both superficial and juxtamedullary segments the reflection coefficients for NaCl and NaHCO3 are less than unity while the reflection coefficients for glucose and alanine were not different from unity. These findings suggest that a small effective osmotic gradient exists across the superficial and juxtamedullary proximal convoluted tubules, and, therefore, part of net sodium transport may be attributed to solvent drag mechanisms.
|Original language||English (US)|
|Number of pages||9|
|Journal||Mineral and Electrolyte Metabolism|
|State||Published - Jan 1 1980|
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism