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Articles in PresS, published online ahead of print May 17, 2002
Am J Physiol Lung Cell Mol Physiol, 10.1152/ajplung.00030.2001
Submitted on January 29, 2001
Accepted on May 7, 2002
1 Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA
* To whom correspondence should be addressed. E-mail: margulie{at}seas.upenn.edu.
Na+-K+-ATPase pumps (Na-pumps) in the alveolar epithelium create a transepithelial Na+ gradient crucial to keeping fluid from the pulmonary airspace. 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 either fibronectin or 5-day conditioned extracellular matrix. After two days in culture cells were uniformly stretched in a custom-made device for 1 hour. Na-pump activity was subsequently assessed by ouabain-inhibitable uptake of rubidium-86, a potassium tracer, and BLM Na-pump abundance was measured. Supporting our hypothesis, cells increased Na-pump activity in a "dose-dependent" manner when stretched to 12%, 25% or 37% change in surface area ([[Delta]]SA), and cells stretched to 25%[[Delta]]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 gadolinium, a stretch-activated channel blocker, amiloride, a sodium channel blocker, or both reduced but did not abolish stretch-induced affects. Sustained tonic stretch, unlike cyclic stretch, elicited no significant Na-pump response.
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