Alveolar epithelial cell mitochondria as source of the surface-active lung lining.

We propose that the surface-active lining of the mammalian lung is formed in the mitochondria of the alveolar epithelial cells. Findings supporting this hypothesis are the presence of strong surfactant uniquely in the washed mitochondrial fraction of mammalian lung, almost complete loss of mitochondrial lamellar forms accompanying loss of lung surface activity after vagotomy, and the absence of strong surface activity from the lung extracts of animals whose alveolar lining cells show no lamellar forms.