Alveolar subphase pH in the lungs of anesthetized rabbits

We measured the pH of the alveolar subphase fluid by puncturing the most superficial alveoli of the exposed lungs of anesthetized rabbits with H+-selective and nonselective KCl microelectrodes. In these experiments, we bathed the lung surface with paraffin oil or buffered Ringer's solutions that had a CO2 tension of 40 Torr (1 Torr = 133.3 Pa) and found an alveolar pH of 6.92 +/- 0.01 (mean +/- sEM). When the pH of the surface buffer was below 6.7 or above 7.5, alveolar pH varied with surface buffer pH. With the nonselective electrode, we did not find a significant electrical potential difference between the alveolar fluid and the pleural surface. These results are consistent with active transport of H+ (or HCO3(-) across alveolar epithelium.