Effects of exposure to acid on alveolar epithelial water and solute transport.

Water and solute transport properties of normal and acid-exposed bullfrog alveolar epithelium were determined under controlled conditions. Paired lungs from the same animal were studied in Ussing chambers. Tissue bioelectric parameters, permeabilities of water and solutes, and hydraulic conductivity were measured. Results from control lungs were compared with those observed after the alveolar epithelium was exposed to acid (pH 2.0-4.0) for variable periods of time (1-60 min). Acid exposure appears to initially damage tissue active transport mechanisms, causing a marked fall in potential difference at pH less than or equal to 3.0. Increases in tissue conductance and permeability to solutes occurred after a variable time lag. Water permeability did not change after acid exposure. Equivalent homogeneous pore radius increased as time of exposure to acid increased. It is concluded that the bullfrog alveolar epithelium, normally resistant to water and solute flux, loses its ability to transport ions actively and gradually becomes leaky after exposure to acid (pH less than or equal to 3.0). The pathway for movement of water across alveolar epithelium may be different from that for solutes.