Airway surface liquid pH in well-differentiated airway epithelial cell cultures and mouse trachea

Airway surface liquid (ASL) pH has been proposed to be important in the pat hophysiology of cystic fibrosis, asthma, and cough. Ratio image analysis wa s used to measure pH in the ASL after staining with the fluorescent pH indi cator 2', 7'- bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-dextran. ASL pH in bovine airway cell cultures grown at an air-liquid interface was 6.98 +/- 0.06 in the absence and 6.81 +/- 0.04 in the presence of HCO3-/CO2 . Steady-state ASL pH changed in parallel to changes in bath pH and was aci dified by Na+ or Cl- replacement but was not affected by the inhibitors ami loride, glibenclamide, or 4,4'-dinitrostilbene-2,2'-disulfonic acid. In res ponse to sudden acidification or alkalization of the ASL by similar to0.4 p H units by HCl/NaOH, ASL pH recovered to its initial value at a rate of 0.0 35 pH units/min (-HCO3-) and 0.060 pH units/min (+HCO3-); the pH recovery r ate was reduced by amiloride and H2DIDS. In anesthetized mice in which the trachea was surgically exposed for measurement of BCECF-dextran fluorescenc e through the translucent tracheal wall, ASL pH was 7.14 +/- 0.01. ASL pH w as sensitive to changes in blood pH created by metabolic (HCl or NaHCO3 inf usion) or respiratory (hyperventilation, hypoventilation) mechanisms. ASL p H is thus primarily determined by basolateral fluid pH, and H+/OH- transpor t between the ASL and basolateral fluid involves amiloride-sensitive Na+/H exchange and stilbene-sensitive Cl-/HCO3- exchange. The rapid response of ASL pH to changes in systemic acid-base status may contribute to airway hyp ersensitivity in asthma and other airway diseases.