AJP - Cell Physiology, Vol 253, Issue 5 C662-C671, Copyright © 1987 by American Physiological Society
Protamine alters apical membrane K+ and Cl- permeability in gallbladder epithelium
S. M. Poler and L. Reuss
Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110.
Protamine addition to the solution bathing the mucosal side of Necturus
gallbladder epithelium (25-100 mg/l) caused depolarization of both cell
membranes, a mucosa-negative change in transepithelial voltage, an increase
in the apical membrane resistance (Ra) followed by a decrease, and a
monotonic increase in transepithelial resistance (Rt). In protamine (25
mg/l), the change in apical membrane voltage elicited by elevating mucosal
solution [K+] from 2.5 to 92.5 mM was reduced from 66 +/-2 to 38 +/- 5 mV
(P less than 0.001). The K+-induced fall in Ra was also reduced in
protamine. These effects could also be elicited by elevating mucosal
solution [K+] simultaneously with the addition of protamine and by
transient addition of protamine during exposure to the high K+ medium. The
effect of protamine on the electrodiffusive Cl- permeability of the apical
membrane (PCl) was studied both in control and forskolin-treated tissues.
In the absence of forskolin, the hyperpolarization of Vmc produced by
lowering mucosal [Cl-] to 10 mM was reversed to a small depolarization; in
forskolin, the initial depolarization produced by lowering [Cl-] was
significantly increased. Finally, exposure to protamine in the absence of
forskolin produced an initial fall in intracellular Cl- activity. Our
results indicate that protamine decreases apical membrane K+ permeability
and increases apical membrane PCl. The time course of the effects of
protamine suggests the possibility of an initial effect on surface
potential, followed by secondary actions mediated by intracellular events.
