Regulation of intracytoplasmic pH and "apparent" intracellular pH in alveolar macrophages

An approach for determining the permeability of cell and subcell membranes to H+/HCO3- has been applied to alveolar macrophages. The approach uses analysis of substrate ratios which are compartment specific and involved in pH-dependent reactions. By determining the changes in substrate pair ratios produced by perturbations of CO2, the effects of intracellular acidosis and alkalosis can be determined. By measuring substrate pair ratios at a constant PCO2 and variable H+/HCO3- it is possible to determine the permeability of the macrophage plasma membrane to these ions qualitatively. Measurements of intracellular lactate/pyruvate ratios showed that the alveolar macrophage plasma membrane is permeable to H+/HCO3-. Previous studies have shown that alveolar macrophages are freely permeable to Cl-. pHi was determined from measurements of pHe and Cli-/Cle- following changes of external PCO2 at a constant HCO3- concentration and following changes in pHe produced by changes of external HCO3- concentration at a constant PCO2. The data show that the relationship between pHi and Phe is: pHi = 0.973 pHe - 0.027 (r = 0.99, P less than 0.001). Thus at pHe = 7.40, macrophage intracellular pHi = 7.17. Alveolar macrophages appear to be permeable to H+/HCO3- and thus resemble erythrocytes, platelets, and lymphocytes and not brain and muscle cells.