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Extramembraneous particles and structural variations of tubular myelin figures in rat lung surfactant
Abstract:
Tubular myelin figures of pulmonary surfactant were examined by electron microscopy after fixation in glutaraldehyde and postfixation in an osmium tetroxide-ferrocyanide mixture. Bilayered membranes were seen as parallel arrays or as lattices with spacings varying from about 36 to 50 nm. This method also produced good visualization of drumstick-like particles, 5 nm in diameter and about 15 nm in length. The particles were regularly spaced at intervals of 16 nm in rows along the rectangular angles of myelin membranes. Depending on the size of the tubules the particles contacted each other in the center of the tubules at low diameters (tubular diameter less than 40 nm) and formed a continuous filamentous central core, or they were separated from one another (tubular diameter greater than 40 nm). In the latter case the central core had a hollow appearance. Based on further findings employing tannic acid, lipid extraction with 2,2-dimethoxypropane, and a ruthenium red-osmium tetroxide technique for the demonstration of polyanionic proteins it is suggested that these particles are protein in nature and that they are involved in the formation and maintenance of the structure of tubular myelin. A new concept of the ultrastructure of tubular myelin figures is proposed.
Insights
Pulmonary surfactant
Area of Science:
- Cell Biology
- Biochemistry
- Pulmonary Medicine
Background:
- Pulmonary surfactant is crucial for lung function.
- Tubular myelin figures are key structures within surfactant.
- Understanding their ultrastructure is vital for respiratory health.
Purpose of the Study:
- To elucidate the ultrastructure of tubular myelin figures.
- To identify the components and their roles in tubular myelin formation.
- To propose a new model for tubular myelin organization.
Main Methods:
- Electron microscopy with glutaraldehyde and osmium tetroxide-ferrocyanide fixation.
- Tannic acid staining.
- Lipid extraction using 2,2-dimethoxypropane.
- Ruthenium red-osmium tetroxide technique for polyanionic proteins.
Main Results:
- Observed bilayered membranes with spacings of 36-50 nm.
- Visualized drumstick-like particles (5 nm x 15 nm) regularly spaced at 16 nm intervals.
- Particles formed continuous cores in small tubules (<40 nm) and hollow cores in larger tubules (>40 nm).
- Evidence suggests particles are proteinaceous and involved in structure maintenance.
Conclusions:
- Proposed a novel concept of tubular myelin ultrastructure.
- Identified protein particles as key structural elements.
- These proteins are implicated in the formation and maintenance of tubular myelin.