Pulmonary alveolar macrophage. Oxidative metabolism of isolated cells and mitochondria and effect of cadmium ion on electron- and energy-transfer reactions

Pulmonary alveolar macrophages (PAMs), obtained by endobronchial lavage of sheep lungs, manifest an endogenous respiration of 9 nmoles of O₂/mg of protein per min at 30°. A phenomenon similar to the Crabtree effect is produced if glucose, oligomycin, or Cd²⁺ is added to a cell suspension and the phenomenon is removed in the presence of an uncoupler or Wurster's blue. Isolated PAM mitochondria oxidize a number of substrates. Typical rates are 67 and 91 nmoles of O₂ per mg of protein per min at 30°, respectively, for α-oxoglutarate and succinate as substrates. These mitochondria characteristically utilize α-glycerophosphate (74 nmoles of O₂/mg of protein per min) but not β-hydroxybutyrate (6 nmoles of O₂/mg of protein per min). Substrate oxidation is completely inhibited by 50 μM Cd²⁺ and also by classical inhibitors of respiration. Cd²⁺ inhibits substrate oxidation presumably by interfering with dehydrogenases of mitochondrial respiratory chain. Isolated PAM mitochondria carry out coupled phosphorylation. The ADP :O ratios are >1 (approaching 2) for flavin-linked substrates and >2 (approaching 3) for pyridine nucleotide linked substrates. This oxidative phosphorylation is sensitive to 2,4-dinitrophenol, oligomycin, and Cd²⁺. A concentration of 5-10 μM Cd²⁺ completely abolishes coupled phosphorylation and respiratory control. Cd²⁺ also inhibits adenosine triphosphatase activity of PAM mitochondria and plasma membrane.