Effects of hyperoxia on type ii cell na,k-atpase function and
expression.
Carter, Ethan P., O. Douglas Wangensteen, Scott M. Oogrady, David H.
Ingbar.
Departments of Physiology, Medicine and Pediatrics, School of
Medicine, University of Minnesota, Minneapolis, MN 55455
APStracts 3:0225L, 1996.
Alveolar fluid is resorbed using active Na& transport primarily
through basolateral Na,K-ATPase and apical sodium channels that are
particularly dense on the alveolar type II (ATII) epithelial cells.
During lung injury with pulmonary edema, continued or accelerated
Na& and fluid resorption is critical for a favorable outcome.
However, little is known of how ATII cell Na& transport is
affected during injury. These experiments examined the effects of
acute lung injury on ATII cell Na,K-ATPase activity and expression
using an established model of rats exposed to 100% O2 for 60 hours.
Na,K-ATPase activity of ATII cells isolated immediately after
exposure was assessed by ouabain-sensitive 86Rb& uptake in intact
cells and by ouabain-sensitive inorganic phosphate production by cell
membranes. In the presence of 1 mM ouabain, ouabain-sensitive Rb&
uptake was not different between normoxic and hyperoxic cells, but
the apparent Na,K-ATPase Vmax of hyperoxic cell membranes was 75 +/-
8% of normoxic membranes (P < 0.05). On Western blots of ATII cell
membranes, [alpha]1-subunit protein significantly decreased with
hyperoxia (35+/-9% of normoxia; P < 0.05), while the amounts of
the [beta]-subunit were unchanged (P > 0.05). On Northern blots of
ATII cell total RNA, steady-state levels of both the [alpha]1- and
b1-subunit mRNA increased following hyperoxia ([alpha]1 = 2.5+/-1.3
fold; b1 = 4.6+/-2.5 fold). Thus despite hyperoxic decreases in Na,K
-ATPase Vmax and the amount of [alpha]1 protein, Rb& uptake by
Na,K-ATPase in intact cells was unchanged. The mRNA levels, protein
amounts, and enzyme activity did not respond in parallel to hyperoxic
injury, and the activity in intact cells correlated best with the
amounts of the beta subunit, the limiting component in de novo pump
assembly in many tissues.
Received 8 April 1996; accepted in final form 30 October 1996.
APS Manuscript Number L112-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996