An oxonol dye is the most potent known inhibitor of band 3-mediated
anion exchange.
Knauf, Philip A., Foon-Yee Law, and Klaus Hahn.
Department of Biophysics, University of Rochester School of
Medicine, Rochester, NY 14642 and *Division of Virology, Department
of Neuropharmacology, Scripps Research Institute, LaJolla, CA
92037
APStracts 2:0262C, 1995.
When cells are acutely exposed to the oxonol dye, bis(1,3
-dibutylbarbituric acid)pentamethine oxonol (diBA), at 0oC, the IC50
(concentration that gives half-inhibition of Cl- exchange) is 0.146
+/- 0.013 [mu]M (N = 12) initially, but the inhibition increases with
time. These characteristics indicate that a rapid initial binding is
followed by a slow conformational change that makes the binding
tighter. If diBA is allowed to equilibrate with band 3, the IC50 is
only 1.05 +/- 0.13 nM (N = 5), making diBA a more potent inhibitor
than DIDS(4,4'-diisothiocyano-stilbene-2,2'-disulfonate), for which
the IC50 under similar conditions is 31 +/- 6 nM (12). Inhibition by
diBA is very slowly reversible at 0oC (t1/2 > 50 h), but the
effect is more readily reversible at higher temperatures. DiBA
competes with DNDS (4,4'-dinitro-stilbene-2,2'-disulfonate) for
inhibition, suggesting an external site of action. In contrast to
DIDS and DNDS, however, increasing Cl- concentrations do not decrease
the inhibitory effect of diBA, indicating that the inhibition is not
competitive. Thus, diBA may be useful for investigating
conformational changes during anion exchange and for stopping
transport without preventing substrate binding. However, when diBA
and other oxonols are used to sense membrane potential, they may have
undesirable side-effects on anion transport processes.
Received 16 September 1994; accepted in final form 3 July 1995.
APS Manuscript Number C557-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.