A Nonselective Cation Channel in Adult Alveolar Epithelial Cells

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 ( I0⁵ M) 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.