Adrenergic regulation of ion transport across adult alveolar epithelial cells: Effects on Cl^- channel activation and transport function in cultures with an apical air interface

The effect of β-adrenergic receptor stimulation on Cl^- channel activation was investigated in alveolar epithelial cells grown in monolayer culture and in freshly isolated cells. Monolayers cultured under apical air interface conditions exhibited enhanced amiloride-sensitive Na⁺ transport compared to apical liquid interface monolayers. Amiloride or benzamil inhibited most (66%) of the basal short circuit current (I_SC) with half-maximal inhibitory concentration (IC₅₀) values of 0.62 μM and 0.09 μM respectively. Basolateral addition of terbutaline (2 μm) produced a rapid decrease in Isc followed by a slow recovery that exceeded the basal Isc. When Cl^- was replaced with methanesulfonate in either intact monolayers or basolateral membrane permeabilized monolayers, the response to terbutaline (2 μM) was completely inhibited. No effect of terbutaline on amiloride-sensitive Na⁺ current was detected. β-Adrenergic agonists and 8-chlorothiophenyl cyclic adenosine monophosphate (8-ctp cAMP) directly stimulated a Cl^- channel in freshly isolated alveolar epithelial cells. The current was blocked by glibenclamide (100 μM) and had a reversal potential of -22 mV. No increase in amiloridesensitve current was detected in response to terbutaline or 8-cpt cAMP stimulation. These data support the conclusion that β-adrenergic agonists produce acute activation of apical Cl^- channels and that monolayers maintained under apical air interface conditions exhibit increased Na⁺ absorption.