AJP - Renal Physiology, Vol 245, Issue 1 123-F129, Copyright © 1983 by American Physiological Society
Video measurement of basolateral membrane hydraulic conductivity in the proximal tubule
L. W. Welling, D. J. Welling and T. J. Ochs
Isolated, lumen-collapsed S1, S2, and S3 proximal tubule segments from the
rabbit were exposed acutely to media made hypotonic or hypertonic by
adjusting the concentration of the impermeant solute raffinose. The result
was a water flux into or out of the cells across their basolateral cell
membranes and a consequent swelling or shrinking of the cells. From tubule
volume changes measured at 1/60-s intervals during the first 0.03-0.2 s of
video recordings, the earliest water fluxes were found to be 0.76 +/- 0.04
nl X min-1 X mm-1 X mosM-1 in S1, 0.53 +/- 0.03 in S2, and 0.35 +/- 0.04 in
S3. When normalized to outer tubule surface areas, these fluxes yield
statistically different hydraulic conductivities of about 5,500, 4,000, and
3,000 microns X s-1 in the three segments. However, when normalized to the
basolateral membrane surface areas, the basolateral membrane hydraulic
conductivities are all approximately 300 microns X s-1 and not
statistically different. If one assumes that the hydraulic conductivities
of the basolateral and apical cell membranes are equal, the latter value
agrees with reported transtubular measurements and is sufficient to allow
nearly isotonic transcellular absorption to occur with driving forces of
2-3 mosM.
