AJP - Cell Physiology, Vol 258, Issue 2 C248-C257, Copyright © 1990 by American Physiological Society
Effect of hyperosmotic challenge on basolateral membrane potential in rabbit urinary bladder
P. J. Donaldson and S. A. Lewis
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
In the rabbit urinary bladder, serosal hyperosmotic challenge (SHOC) with
either 33 mM NaCl or 66 mM mannitol caused basolateral membrane potential
(Vbl) to initially depolarize from -52.6 +/- 1.6 to -48.4 +/- 1.4 mV,
followed by a recovery of Vbl to -57.5 +/- 1.3 mV after 13.7 +/- 1.0 min.
The voltage recovery was dependent on both serosal HCO3- and Cl-, and in
the absence of both, Vbl depolarized to -11.6 +/- 1.5 mV and the ratio of
apical-to-basolateral resistance (Ra/Rbl) decreased from 21.0 +/- 3.4 to
8.3 +/- 3.1. This decrease in Ra/Rbl and consequent depolarization of Vbl
is caused by a decrease in basolateral K+ conductance. Replacement of
serosal Cl- with NO3- or SCN- followed by SHOC caused a sustained
depolarization of Vbl to -32.5 +/- 4.4 and -40.9 +/- 0.9 mV, respectively.
However, when Br- was used to replace Cl-, voltage recovery occurred but
was slowed (24.0 +/- 2.7 min) and reduced in magnitude (-47.5 +/- 3.5 mV).
Addition of amiloride (1 mM) or niflumic acid (100 microM), but not
bumetanide (1 microM), to the serosal bathing solution inhibited voltage
recovery causing Vbl to depolarize to -36.3 +/- 2.6 and -41.5 +/- 4.5 mV,
respectively. Serosal addition of ouabain after SHOC caused Vbl to
depolarize by 10.8 +/- 0.9 mV in 2 min. We speculate that the SHOC-induced
initial depolarization of Vbl is a loss of Ba2(+)-sensitive K+ conductance
caused by cell shrinkage. The subsequent repolarization/hyperpolarization
of Vbl is caused by an enhanced basolateral membrane Na+ pump current and a
reappearance of the Ba2(+)-sensitive K+ conductance. The parallel operation
of Na(+)-H+ and Cl(-)-HCO3- exchanges will then supply Na+ for the pump
current and, via cellular accumulation of Na+, K+, and Cl-, might result in
a partial recovery of cell volume and thus Ba2(+)-sensitive K+ conductance.
