AJP - Renal Physiology, Vol 251, Issue 2 319-F333, Copyright © 1986 by American Physiological Society
Electrophysiology of salamander proximal tubule. I. Effects of rapid cooling
H. Sackin
The response of the amphibian proximal tubule to a rapid decrease in
temperature was studied in isolated perfused tubules of Ambystoma tigrinum.
Cooling from 23 to 4 degrees C increased paracellular and cellular
electrical resistances by factors of 1.7 and 3.6, respectively, but had
virtually no effect on the ionic selectivity of the paracellular pathway.
When lumen and bath solutions were maintained identical by rapid tubule
perfusion, decreasing bath temperature from 22 to 0 degree C in 400 ms
depolarized the transepithelial potential (Vte) from -3.7 +/- 0.3 to -1.1
+/- 0.2 mV and depolarized the basolateral membrane potential (Vbl) from
-52 +/- 3 to -45 +/- 3 mV (n = 12). These fast depolarizations were
followed by slower depolarizations of both Vte and Vbl that continued
throughout the period of low temperature. Only approximately 30% of the
initial slow depolarization of Vte at low temperature could be explained by
changes in electrical resistance and cell membrane potential. The remaining
70% of this Vte depolarization at low temperature is consistent with
equilibration of a hypertonic interspace with isotonic lumen and bath
solutions. Given the anion selectivity of Ambystoma proximal tubule, the
magnitude of this slow Vte depolarization implies an interspace NaCl
concentration 2-5% higher than the NaCl concentration in either the lumen
or bath solutions.
