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Pathways through the intercellular clefts of frog mesenteric capillaries
1Department of Physiology & Biophysics, St Mary's Hospital Medical School, Imperial College of Science, Technology & Medicine, London.
The Journal of Physiology
|July 1, 1993
Summary
This study reveals the ultrastructure of frog capillary endothelial intercellular clefts, showing they have narrow regions and occasional gaps that influence hydraulic permeability (Lp). Lanthanum tracer experiments identified these gaps as pathways for solute passage.
Area of Science:
- Cell Biology
- Physiology
- Microcirculation Research
Background:
- Understanding endothelial intercellular clefts is crucial for comprehending microvascular permeability.
- The precise structural basis for hydraulic permeability (Lp) in capillaries remains an area of active investigation.
Purpose of the Study:
- To elucidate the three-dimensional ultrastructure of endothelial intercellular clefts in frog mesenteric capillaries.
- To correlate capillary ultrastructure with measured hydraulic permeability (Lp) and the passage of extracellular tracers.
Main Methods:
- Determined hydraulic permeability (Lp) of frog mesenteric capillaries perfused with Ringer solution and albumin.
- Utilized lanthanum nitrate as an electron-dense tracer to identify open pathways in intercellular clefts.
- Employed serial section electron microscopy to reconstruct the three-dimensional ultrastructure of clefts.
Main Results:
- Capillary intercellular clefts exhibit continuous narrow regions interspersed with occasional wider discontinuities.
- Lanthanum tracer filled clefts up to tight junctions, with occasional complete passage through discontinuities.
- The outer leaflets of adjacent endothelial cells at tight junctions were separated by a small gap (approx. 2.3 nm).
Conclusions:
- The structural features of intercellular clefts, including narrow regions and specific discontinuities, dictate capillary hydraulic permeability.
- Lanthanum tracer successfully mapped solute pathways, confirming the role of cleft discontinuities in permeability.
- The findings provide detailed ultrastructural insights into the mechanisms governing microvascular exchange.