Tight junctional permeability in living cells: dynamic changes directly visualized by confocal laser microscopy

Area of Science:

• Physiology
• Cell Biology
• Microscopy

Background:

• Tight junctions regulate paracellular transport in salivary glands.
• Understanding their dynamic permeability is crucial for glandular function.

Purpose of the Study:

• To investigate the dynamic permeability of tight junctions in rat parotid and submandibular glands.
• To determine how secretagogues and other factors influence paracellular passage of molecules.

Main Methods:

• Confocal microscopy was employed to visualize fluorescent tracers (Lucifer Yellow, Propidium Iodide, dextrans) in living rat salivary glands.
• Tracers of various molecular weights and charges were used to assess paracellular pathway integrity.
• Secretion was induced using isoproterenol and carbachol; other conditions like anoxia and cytochalasin D were also tested.

Main Results:

• In normal glands, tracers did not reach the lumen. Upon stimulation, tracers permeated the tight junctions into the lumen within minutes.
• Permeability changes were reversible, with luminal fluorescence disappearing after secretagogue removal.
• Different molecular weight limits for paracellular passage were observed with isoproterenol (40K) and carbachol (10K), with minimal charge selectivity.
• Anoxia, cell dissociation, and cytochalasin D also induced luminal fluorescence.

Conclusions:

• Salivary gland tight junctions exhibit dynamic permeability, modulating the passage of molecules through the paracellular pathway.
• Factors such as oxygen supply, extracellular matrix, and cytoskeleton likely play regulatory roles in tight junction permeability.