Electrophysiological characterization of rat type II pneumocytes in situ.
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 microM and 1 mM of amiloride, respectively. Exposure of slices to 0.5 microM dexamethasone for 1 hour did not affect ion currents, while chronic exposure (0.5 microM, 24-72 h) induced an increase in both total Na+-entry currents and amiloride-sensitive currents. Under acute exposure to 100 microM 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 microM 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.
Shlyonsky
Vadim
V
Université Libre de Bruxelles, Laboratoire de Physiologie et Physiopathologie, Campus Erasme, CP 604, 808 Route de Lennik, 1070 Bruxelles, Belgium. vshlyons@ulb.ac.be
Goolaerts
Arnaud
A
Mies
Frédérique
F
Naeije
Robert
R
D000818:Animals; D002470:Cell Survival; D002712:Chlorides / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D004594:Electrophysiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009761:Nystatin / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D011652:Pulmonary Circulation; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000502:physiology*
D002712:Chlorides; D009761:Nystatin; D003907:Dexamethasone; D012964:Sodium