Ultrahistochemical investigations of dog lung surfactant with ruthenium red and iodoplatinate reactions.

Dog lungs have been fixed by immersion and submitted to two histochemical procedures. An iodoplatinate reaction technique to demontrate choline phospholipids stains cell membranes, inclusion bodies of type II alveolar epithelial cells and tubular myelin figures of pulmonary surfactant, the latter as electron-dense lines measuring 5 nm. The ruthenium red procedure gives rise to an intense contrast of the free surface of alveolar epithelium. The 5 nm-lines of the pulmonary surfactant are seen as electron-lucent lines, but bordered by electron-dense rims. Though both techniques have limitations in their interpretation, which are discussed in this paper, they demonstrate the tubular myelin figures to be a highly organized mixture of phospholipids and glycoproteins.