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Molecular sieve in rat glomerular basement membrane as revealed by negative staining
Abstract:
Human and bovine glomerular basement membranes (GBM) were previously shown to be a three-dimensional molecular sieve composed of pores and strands by negative staining and electron microscopy. In this study, rat GBM were isolated under several different conditions to rule out morphological changes due to isolation procedures. Rat GBM isolated under different conditions all showed the same morphological features as bovine and human GBM. The strands forming the molecular sieve were almost equal in width, measuring approximately 3.1 +/- 0.8 nm. Pores were oval or polygonal. The size of pores varied a little averaging 4.4 +/- 1.0 nm in the long dimension and 3.0 +/- 0.6 nm in the short dimension. The average density of the pores was 16 +/- 2/1,000 nm2. Negative staining demonstrated pores in isolated and unfixed GBM, indicating that the function of GBM is mechanical filtration of macromolecules on the basis of size.
Insights
Rat glomerular basement membranes (GBM) act as a molecular sieve, filtering macromolecules by size. Electron microscopy revealed consistent pore and strand structures across different isolation methods, confirming GBM
Area of Science:
- Nephrology
- Cell Biology
- Biophysics
Background:
- Glomerular basement membranes (GBM) are crucial for kidney filtration.
- Previous studies using human and bovine GBM suggested a molecular sieve structure.
- The role of isolation procedures on GBM morphology was not fully understood.
Purpose of the Study:
- To investigate the morphology of rat glomerular basement membranes (GBM).
- To determine if isolation procedures affect GBM structure.
- To confirm the molecular sieve function of GBM.
Main Methods:
- Isolation of rat GBM under various conditions.
- Negative staining and electron microscopy.
- Morphological analysis of GBM structure, including strands and pores.
Main Results:
- Rat GBM exhibited consistent morphological features regardless of isolation method.
- Strands measured approximately 3.1 +/- 0.8 nm in width.
- Pores were oval/polygonal, averaging 4.4 +/- 1.0 nm (long axis) and 3.0 +/- 0.6 nm (short axis), with a density of 16 +/- 2/1,000 nm2.
Conclusions:
- Rat GBM structure is robust and not significantly altered by isolation procedures.
- The observed pore and strand architecture supports a mechanical filtration mechanism.
- GBM functions as a size-selective filter for macromolecules.