Redox state of free nicotinamide-adenine nucleotides in the cytoplasm and mitochondria of alveolar macrophages

Cytoplasmic free NAD⁺/NADH ratios have been calculated from lactate to pyruvate ratios, and mitochondrial NAD⁺/NADH ratios, have been calculated from β-hydroxybutyrate to acetoacetate ratios in isolated rabbit alveolar macrophages. In freshly harvested cells, assuming a pH of 7 for the two compartments, cytoplasmic NAD⁺/NADH averaged 709 ±293 (SD), and mitochondrial NAD⁺/NADH averaged 33.2 ±30.2, values which are significantly different. 30 min of air incubation in a relatively poorly buffered medium showed a significant reduction in calculated mitochondrial NAD⁺/NADH to 10.1 ±4.8. 30 min of exposure of cells to a hypoxic environment (equivalent to a nonventilated, perfused alveolus) caused significant reductions of NAD⁺/NADH in both compartments. Re-exposure of hypoxic cells to air produced a change toward normal in cytoplasmic NAD⁺/NADH but did not reverse mitochondrial abnormality. Uncertainties concerning the value of cytoplasmic and mitochondrial pH under control conditions and during experimental pertubations, limit absolute interpretation of NAD⁺/NADH ratios calculated from redox pairs, but the data suggest the following: (a) separate cytoplasmic and mitochondrial compartments for NAD⁺ and NADH exist in the alveolar macrophage; (b) brief periods of exposure to moderate hypoxia of the degree seen in clinical lung disease produce decreases in both cytoplasmic and mitochondrial NAD⁺/NADH; (c) the mitochondrial changes are less easily reversed than the cytoplasmic changes; (d) measurements of NAD⁺/NADH provide an early sensitive indication of biochemical abnormality; and (e) careful control of extracellular pH is required in studies involving experimental modifications of alveolar macrophage function.

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