Calcium site specificity. Early Ca2+-related tight junction events

Area of Science:

• Cell Biology
• Biophysics
• Physiology

Background:

• The molecular mechanisms governing the interaction of calcium (Ca2+) and metal ions with binding sites that regulate tight junctions (TJs) remain incompletely understood.
• Investigating these interactions is crucial for understanding epithelial and endothelial barrier function.

Purpose of the Study:

• To elucidate the roles of Ca2+ and various metal ions in modulating tight junction permeability and seal.
• To utilize metal ions as probes to characterize Ca2+-binding sites associated with tight junctions.

Main Methods:

• Employing the frog urinary bladder model to study tight junction dynamics.
• Manipulating basolateral Ca2+ concentrations and introducing various divalent metal ions (Mg2+, Ba2+, Mn2+, Cd2+, La3+) to assess their effects on TJ integrity and recovery.

Main Results:

• Extracellular Ca2+ withdrawal reversibly opens TJs; Ca2+ repletion restores the TJ seal.
• Mg2+ and Ba2+ do not maintain TJ seal or promote recovery; Mg2+ inhibits Ca2+-induced recovery.
• Mn2+ and Cd2+ act as Ca2+ agonists, preventing TJ opening and promoting recovery (Mn2+) or stabilizing closed TJs with toxicity (Cd2+).
• La3+ increases TJ permeability in the presence of Ca2+, indicating high affinity for Ca2+-binding sites.

Conclusions:

• Ca2+ and specific metal ions directly interact with binding sites to regulate TJ permeability.
• The findings suggest potential interactions with E-cadherin.
• La3+ can disrupt TJs even in the presence of Ca2+, necessitating caution in its use for permeability studies.