Ridge KM, Olivera WG, Saldias F, Azzam Z, Horowitz S, Rutschman DH, Dumasius V, Factor P, Sznajder JI. Alveolar type 1 cells express the alpha2 Na,K-ATPase, which contributes to lung liquid clearance.
Circ Res 2003;
92:453-60. [PMID:
12600893 DOI:
10.1161/01.res.0000059414.10360.f2]
[Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The alveolar epithelium is composed of alveolar type 1 (AT1) and alveolar type 2 (AT2) cells, which represent approximately 95% and approximately 5% of the alveolar surface area, respectively. Lung liquid clearance is driven by the osmotic gradient generated by the Na,K-ATPase. AT2 cells have been shown to express the alpha1 Na,K-ATPase. We postulated that AT1 cells, because of their larger surface area, should be important in the regulation of active Na+ transport. By immunofluorescence and electron microscopy, we determined that AT1 cells express both the alpha1 and alpha2 Na,K-ATPase isoforms. In isolated, ouabain-perfused rat lungs, the alpha2 Na,K-ATPase in AT1 cells mediated 60% of the basal lung liquid clearance. The beta-adrenergic agonist isoproterenol increased lung liquid clearance by preferentially upregulating the alpha2 Na,K-ATPase protein abundance in the plasma membrane and activity in alveolar epithelial cells (AECs). Rat AECs and human A549 cells were infected with an adenovirus containing the rat Na,K-ATPase alpha2 gene (Adalpha2), which resulted in the overexpression of the alpha2 Na,K-ATPase protein and caused a 2-fold increase in Na,K-ATPase activity. Spontaneously breathing rats were also infected with Adalpha2, which increased alpha2 protein abundance and resulted in a approximately 250% increase in lung liquid clearance. These studies provide the first evidence that alpha2 Na,K-ATPase in AT1 cells contributes to most of the active Na+ transport and lung liquid clearance, which can be further increased by stimulation of the beta-adrenergic receptor or by adenovirus-mediated overexpression of the alpha2 Na,K-ATPase.
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