The influence of amphotericin b on the sodium pump of porcine lens
epithelium.
Delamere, Nicholas A., William L. Dean, Jeffrey M. Stidam, Amy E.
Moseley.
Department of Ophthalmology and Visual Sciences and Department of
Biochemistry, University of Louisville, Louisville, KY 40292
APStracts 2:0293C, 1995.
Active transport by Na,K-ATPase in the monolayer of lens epithelium is
vital for the regulation of sodium and potassium levels within the
mass of fiber cells that make up the bulk of the lens. In this study,
experiments were conducted using porcine lenses to test whether Na,K
-ATPase activity in the epithelium is altered when the permeability of
lens cell plasma membranes is increased by the ionophore amphotericin
B. After 24 hr sodium was significantly (p < 0.01) elevated in
lenses exposed to 5[mu]M or 10[mu]M amphotericin B. Amphotericin B
stimulated 86Rb uptake, probably through an increase of cytoplasmic
sodium concentration due to increased inward sodium leak; the rate of
ouabain-sensitive potassium (86Rb) uptake by intact lenses was
significantly increased by amphotericin B at 5[mu]M (p < .05)
and 10[mu]M (p < .01). After 24 hr, the epithelium from lenses
exposed to amphotericin B had an Na,K-ATPase activity which was
> 2 fold higher (p < 0.01) than the Na,K-ATPase activity in
control lenses. By immunoblot, there was an increase in Na,K-ATPase
catalytic ([alpha]) subunit immunoreactive polypeptide in the
epithelium of lenses exposed to amphotericin B. The increase stemmed
from a marked increase of Na,K-ATPase [alpha]2 immunoreactive
polypeptide but little change in the amount of [alpha]1
immunoreactive protein. As judged by immunoblot experiments, the
amount of Na,K-ATPase 1 immunoreactive polypeptide also appeared to
be higher in the epithelium of amphotericin B-treated lenses compared
to control lenses. In summary, these results suggest that in response
to a permeability challenge with amphotericin B, the porcine lens
epithelium is able to increase the activity of Na,K-ATPase. The same
permeability challenge also appears to stimulate the biosynthesis of
Na,K-ATPase catalytic subunit as well as glycoprotein subunit
polypeptides.
Received 18 October 1994; accepted in final form 3 August 1995.
APS Manuscript Number C618-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.