AJP - Renal Physiology, Vol 253, Issue 2 290-F298, Copyright © 1987 by American Physiological Society
Video measurement of basolateral NaCl reflection coefficient in proximal tubule
L. W. Welling, D. J. Welling and T. J. Ochs
Isolated, lumen-collapsed, proximal and distally occluded segments of
rabbit S1 and S2 proximal tubule were equilibrated in isotonic NaCl or
isosmotic raffinose medium and then exposed acutely to hypotonic or
hypertonic raffinose or NaCl solution. The result was a water flux per
millimeter tubule length, JVo, across the basolateral cell membranes and a
consequent cell swelling or shrinkage that could be measured by a video
technique in the initial 0.1 s or less after a change from steady state.
The cell volume change was proportional to the applied osmolality
difference, delta pi, and differed consistently with the solute employed.
From the equation JVo/delta pi = sigma LpA, where sigma is the basolateral
membrane reflection coefficient for the osmotic solute used and LpA is the
membrane hydraulic conductivity per millimeter tubule length, and from the
assumption that sigma raffinose = 1, sigma NaCl was obtained by dividing
the JVo/delta pi values from the NaCl studies by those from the raffinose
studies. For both S1 and S2 segments, sigma NaCl was found to be
approximately 0.5. A similar value was obtained from the rate of cell
shrinkage immediately after isosmolar exchange of raffinose for NaCl
medium.
