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ARTIFACTUAL LOCALIZATION OF FERRITIN IN THE CILIARY EPITHELIUM IN VITRO.
1Biological Laboratories, Harvard University, Cambridge, Massachusetts, and The Wilmer Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland. Dr. Tormey is now at The Johns Hopkins University School of Medicine.
The Journal of Cell Biology
|October 30, 2009
Summary
Electron microscopy revealed ferritin accumulation in rabbit ciliary epithelium. Osmium tetroxide fixation increased plasma membrane permeability, causing artifacts and misleading pinocytosis interpretations.
Area of Science:
- Ocular Biology
- Cell Biology
- Biochemistry
Background:
- Ferritin is an iron-storage protein crucial for cellular iron homeostasis.
- The ciliary epithelium plays a vital role in aqueous humor production and ocular physiology.
- Understanding tracer particle uptake mechanisms is essential for interpreting experimental results.
Purpose of the Study:
- To investigate the in vitro accumulation of ferritin by the ciliary epithelium of adult albino rabbits.
- To differentiate between passive diffusion and active transport (pinocytosis) of tracer particles.
- To identify potential artifacts introduced by fixation and embedding procedures.
Main Methods:
- In vitro study using adult albino rabbit ciliary epithelium.
- Electron microscopy for high-resolution visualization of ferritin.
- Osmium tetroxide fixation and Araldite embedding for cell preservation.
Main Results:
- Ferritin was observed in three distinct locations: apparent vesicles, cytoplasmic matrix, and basement membrane.
- Tracer particles were found free in the cytoplasmic matrix, suggesting diffusion.
- The appearance of ferritin in vesicles did not confirm pinocytosis.
Conclusions:
- Osmium tetroxide fixation significantly enhances plasma membrane permeability.
- This increased permeability allows for passive diffusion of tracer particles, mimicking active uptake.
- Colloidal particles used as tracers can lead to artifactual interpretations, particularly regarding pinocytosis.
