AJP - Cell Physiology, Vol 257, Issue 3 C568-C578, Copyright © 1989 by American Physiological Society
Electrophysiological effects of mucosal Cl- removal in Necturus gallbladder epithelium
J. S. Stoddard and L. Reuss
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77550.
The factors responsible for the cell membrane hyperpolarization elicited in
Necturus gallbladder epithelium on Cl- removal from the mucosal bathing
solution were evaluated with conventional and ion-sensitive microelectrode
techniques. Cl- removal causes reversal of apical Cl- -HCO3- exchange,
resulting in a fall in intracellular Cl- activity (aiCl) and an increase in
intracellular pH (pHi). Concomitantly, the cell membranes hyperpolarize to
values close to the K+ equilibrium potential (EK), aiNa falls, and aiK
rises. The observed changes in membrane voltage are not attributable to a
pHi-dependent increase in cell membrane K+ permeability (PK), because 1)
the cell membrane resistances increased and 2) elevating solution partial
pressure of CO2 (PCO2) to counterbalance the cellular alkalinization on
mucosal Cl- removal caused a further hyperpolarization of the cell
membranes to values greater than EK. This additional hyperpolarization was
related to the activity of the Na+ pump, inasmuch as it was accompanied by
an increase in aiNa and was ouabain sensitive. These results are consistent
with, but do not prove, pump electrogenicity. During the period of Cl-
removal from the mucosal bathing solution, the cell membrane depolarization
caused by raising serosal K+ concentration was increased, whereas the
depolarization caused by lowering serosal Cl- concentration was decreased,
compared with substitutions under control conditions. These results
indicate that mucosal Cl- removal causes a decrease in basolateral PCl,
which we speculate could be due to a decrease in cell volume. We conclude
that the hyperpolarization of the cell membranes on mucosal Cl- removal is
primarily due to the combined effects of the fall in basolateral PCl and
the increase in basolateral ECl.
