Abstract
OBJECTIVE: Efficient gas exchange across the alveolar membrane requires a dry air space. At birth, active Na+transport provides the major driving force for absorption of fetal lung liquid, and during adult life, similar transport mechanisms balance fluid exchange across the alveolarcapillary membrane. A cation channel, previously identified in fetal alveolar epithe lium, may represent one of several pathways which regulate apical-basal transepithelial Na+flux. The purpose of this study was to determine if cation channels are also present in adult alveolar epithelial cells.DESIGN: Standard inside-out patch-clamp recording techniques were used to study channels present in patches of membrane from adult rat alveolar epithelium.POPULATION: Alveolar epithelial cells were obtained from adult male Sprague-Dawley rats and studied in primary cell culture.MAIN RESULTS: A 23 pS nonselective cation channel was identified in 68% of patches voltage clamped to -60 mV. The probability of channel opening was not influenced by changes in membrane potential. Amiloride ( I05M) applied to the extracellular membrane induced channel flickering and reduced the apparent mean channel open time without affecting channel conductance.CONCLUSIONS: These results provide direct evidence for a cation channel in the apical membrane of adult alveolar epithelial cells. The channel is similar to a nonselective cation channel in fetal alveolar epithelial cells and may play an important role in Na+-coupled fluid absorption and/or K+secretion.
Highlights
Adult alveolar epithelial cells grown on a collagen matrix adopted a typical 'cobblestone' appearance when examined using inverted light microscopy
T his is due, in part, to difficulties experienced by ourselves and others in obtaining high quality recording conditions with primary epithelial cells grown in dissociated cell cultures [27]
The probability of channel opening was insensitive to changes in membrane potential and amiloride-induced channel flickering and reduced channel open time
Summary
Efficie nt gas exchange across the alveolar membrane requires a dry air space. At birth, active Na+ transport provides the major driving force for absorption of fetal lung liquid, and during adult life, similar transport mechanisms balance fluid exchange across the alveolarcapillary membrane. CONCLUSIONS: These results provide direct e vidence for a cation channel in the apical membrane of adult alveolar epithelial cells. Fetal and adult alveolar epithelial cells form 'tight' , high resistance membranes and generate an amiloride-sensitive, Na+-dependent, shortcurcuit current [9,10,11]. These data indicate that alveolar epithelial cells have the bioelectric characteristics necessary for active ion transport ( 12). Part of this work was previously published in abstract form ( 17)
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