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Electrophysiological Characterization of Rat Type II Pneumocytes in Situ

¹ Université Libre de Bruxelles, Brussels, Belgium

Correspondence and requests for reprints should be addressed to Dr. Shlyonsky Vadim, Université Libre de Bruxelles, Laboratoire de Physiologie et Physiopathologie, Campus Erasme, CP 604, 808, route de Lennik, 1070 Bruxelles, Belgium. E-mail: vshlyons{at}ulb.ac.be

Optimal aeration of the lungs is dependent on an alveolar fluid clearance, a process that is governed by Na⁺ and Cl^– transport. However, the specific contribution of various ion channels in different alveolar cell types under basal or stimulated conditions is not exactly known. We established a novel functional model of rat lung slices suitable for nystatin-perforated whole-cell patch-clamp experiments. Lung slices retained a majority of live cells for up to 72 hours. Type II pneumocytes in situ had a mean capacitance of 8.8 ± 2.5 pF and a resting membrane potential of –4.4 ± 1.9 mV. Bath replacement of Na⁺ with NMDG⁺ decreased inward whole-cell currents by 70%, 21% and 52% of which were sensitive to 10 µM and 1 mM of amiloride, respectively. Exposure of slices to 0.5 µM dexamethasone for 1 hour did not affect ion currents, while chronic exposure (0.5 µM, 24–72 h) induced an increase in both total Na⁺-entry currents and amiloride-sensitive currents. Under acute exposure to 100 µM cpt-cAMP, Type II cells in situ rapidly hyperpolarized by 25-30 mV, due to activation of whole-cell Cl^–-currents sensitive to 0.1 mM of 5-Nitro-2-(3-phenylpropylamino)benzoic acid. In addition, in the presence of cpt-cAMP, total sodium currents and currents sensitive to 10 µM amiloride increased by 32% and 70%, respectively. Thus, in Type II pneumocytes in situ: (1) amiloride-sensitive sodium channels contribute to only half of total Na⁺-entry and are stimulated by chronic exposure to glucocorticoids; (2) acute increase in cellular cAMP content simultaneously stimulates the entry of Cl^– and Na⁺ ions.

Key Words: alveolar epithelium • ion transport • amiloride • patch-clamp

CLINICAL RELEVANCE The findings described in this article contribute to understanding the ion transport function by lung alveolar cells in their native environment.