title: Nature, origin and fates of membranous lamellae in the lung of the neonate rat.
abstract: This study explores the basic nature and formation of lamellar accumulations in the vertebrate lung, and the problematical interrelationship of the lamellae with mitochondria. Autolysosomes are a constant feature of the type II alveolar pneumonocyte of the 2-day-old rat. They are characterized by a single boundary membrane, enclosing a heterogeneous collection of vesicles and membraneous lamellae. The autolysosomes result from repeated episodes of glycogen catabolism, and eventually transform into osmiophilic lamellated bodies. Membranous lamellae within autolysosomes and lamellated bodies represent isolating membranes of cellular autophagy, emptied of their digested contents. Proliferated isolating membranes themselves undergo lysis, providing recycled constituents for the differentiating or dividing cell. Mitochondria of the type II alveolar cell often display invaginations occupied by membranous masses; these masses are demonstrated by high magnification electron micrographs to be continuous with and derived from lamellated bodies, a new finding. Inner mitochondrial membranes lining the invaginations are thinned and crista-free. It is concluded that undergraded or partially lysed isolating membranes follow either of two cellular pathways: they may be eliminated from the cell into the alveolar cavity, or may fill mitochondrial indentations.
authors.affiliation: Department of Zoology, University of Canterbury, Christchurch, New Zealand.
authors.forename: J B
authors.initials: JB
authors.lastname: Williams
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000033:anatomy & histology*; D007425:Intracellular Membranes / Q000648:ultrastructure*; D008168:Lung / Q000648:ultrastructure*; D008928:Mitochondria / Q000648:ultrastructure*; D015388:Organelles / Q000648:ultrastructure*; D051381:Rats