AJP - Renal Physiology, Vol 251, Issue 2 334-F347, Copyright © 1986 by American Physiological Society
Electrophysiology of salamander proximal tubule. II. Interspace NaCl concentrations and solute-coupled water transport
H. Sackin
The role of the paracellular interspace in solute-coupled water transport
was investigated in isolated perfused salamander (Ambystoma) proximal
tubules using a null-point technique to estimate interspace NaCl
concentrations. Constant composition of luminal fluid was maintained by
rapid (200 nl/min) perfusion of tubules 600,micron or less in length.
Inhibition of active transport by a decrease in bath temperature from 22 to
0 degrees C in 400 ms produced rapid depolarizations of both the
transepithelial (Vte) and basolateral (Vbl) potential, followed by slower
changes in potential that occurred at low temperature. During this period,
the time course of Vbl was independent of small changes in bath NaCl
concentration, whereas the time course of Vte at low temperature varied
from a slow depolarization to a slow repolarization depending on whether
the concentration of NaCl in the bath equaled or exceeded that in the
perfusate. Absence of a slow change in Vte at low temperature indicated a
match between the NaCl concentration of the interspace and the test
concentration of NaCl in the bath. Using this technique with 12 tubules,
the normal interspace NaCl concentration appeared to be approximately 4%
above the NaCl concentration of either the lumen or bath, demonstrating
that the interspace of the salamander proximal tubule can function as a
local hyperosmotic compartment to facilitate fluid transport between
solutions of identical composition.
