Electron Microscopic Studies of the Lung of the Salamander, Hynobius nebulosus:

II. Osmiophilic Lamellar Bodies and Alveolar Surfactant

Abstract

Lamellar bodies in the lung of salamanders, Hynobius Nebulosus, are concentrically lamellated, round, oval, or sometimes elongated bodies and divided into two types morphologically. The first type is an evenly lamellate body and found mainly in the respiratory epithelial cell. It might originate from mitochondria because of having a double membrane structure in the outermost layer of its immature type. The second type is composed of an outer highly dense layer with compact lamellar structures and an inner, less dense layer with more loose lamellae, being observed in the ciliated cells. It has no double membrane in the outermost layer. Sometimes, abundant small immature bodies of the second type are observed close to the Golgi lamellae or vacuoles some of which contain a highly dense material. The second type of lamellar body might arise from the Golgi Apparatus. A modified first type which resembles the first type but differs in detail, occurs in the mucous cell. With maturing, in the first type and some of the modified first type the entire lamellae become loose, but in the second type and some of the modified first type only the inner layer does, and the outer dense layer remains unchanged. Thus matured lamellar bodies are released into the alveolar space by exocytosis. The released lamellar bodies first retain to some degree the structures characteristic of each type, and especially, the dense outer layer shows a crystalloid structure, which consists of parallel straight lamellae placed at right angles toward the outer surface. Loose lattice-like structures, which seem to correspond to tubular myelin, were occasionally observed in the inner layer of some secreted lamellar bodies with an outer dense layer. In addition, some membranes composing the loose lattice-like structure are directly continuous with the membranes derived from the crystalloid. These results suggest that the surfactant of the lung of Hynobius nebulosus contains tubular myelin and that the tubular myelin may originate from the outer compact layer of type II and/or modified type I lamellar bodies.