AJP - Renal Physiology, Vol 259, Issue 4 594-F597, Copyright © 1990 by American Physiological Society
Relative osmotic effects of raffinose, KCl, and NaCl across basolateral cell membrane
L. W. Welling, D. J. Welling and T. Ochs
Research Service, Veterans Administration Medical Center, Kansas City, Missouri 64128.
Lumen-collapsed segments of rabbit S2 proximal tubule were bathed in
isotonic medium and then exposed acutely to a medium made hypertonic by the
addition of raffinose, NaCl, KCl, Na gluconate, K gluconate, or choline Cl.
The result was a rapid efflux of water and a shrinking of the tubule, which
could be measured by video techniques within the first 0.1 s. After
reequilibration in isotonic medium, each tubule was then exposed to a
second hypertonic medium to provide a direct comparison between two
different solutes, either NaCl vs. KCl or raffinose vs. any one of the
other solutes. Because raffinose is impermeant across the basolateral cell
membrane, the ratio of its effect to that of another solute is a measure of
the reflection coefficient (sigma) of that other solute. The following
results were obtained: sigma KCl = 0.70 +/- 0.02, sigma K gluconate = 0.97
+/- 0.07, sigma Na gluconate = 0.84 +/- 0.06, and sigma choline Cl = 0.75
+/- 0.06. We previously have reported sigma NaCl = 0.56 +/- 0.07. If sigma
of each salt is considered to be the arithmetic average of its component
parts, and if gluconate and choline are considered to be impermeant, we
also obtain sigma Na+ = 0.68, sigma K+ = 0.94, and sigma Cl- = 0.50.
