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Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104
Na+-K+-ATPase
pumps (Na+ pumps) in the alveolar epithelium create a
transepithelial Na+ gradient crucial to keeping fluid from
the pulmonary air space. We hypothesized that alveolar epithelial
stretch stimulates Na+ pump trafficking to the basolateral
membrane (BLM) and, thereby, increases overall Na+ pump
activity. Alveolar type II cells were isolated from Sprague-Dawley rats
and seeded onto elastic membranes coated with fibronectin or
5-day-conditioned extracellular matrix. After 2 days in culture, cells
were uniformly stretched for 1 h in a custom-made device. Na+ pump activity was subsequently assessed by
ouabain-inhibitable uptake of 86Rb+, a
K+ tracer, and BLM Na+ pump abundance was
measured. In support of our hypothesis, cells increased Na+
pump activity in a "dose-dependent" manner when stretched to 12, 25, or 37% change in surface area (
SA), and cells stretched to 25%
SA more than doubled Na+ pump abundance in the BLM.
Cells on 5-day matrix tolerated higher strain than cells on fibronectin
before the onset of Na+ pump upregulation. Treatment with
Gd3+, a stretch-activated channel blocker, amiloride, a
Na+ channel blocker, or both reduced but did not abolish
stretch-induced effects. Sustained tonic stretch, unlike cyclic
stretch, elicited no significant Na+ pump response.
ventilator-induced lung injury; alveolar edema; Na+-K+- ATPase; mechanical deformation; rubidium-86
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