Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Area of Science:

• Biophysics
• Cell Biology
• Molecular Biology

Background:

• Connexin 26 (Cx26) forms gap junctions crucial for cell-to-cell communication.
• Elevated carbon dioxide (CO2) levels can influence cellular functions.
• Cx26 hemichannels are known to open in response to CO2.

Purpose of the Study:

• To investigate the effect of CO2 on Cx26 gap junction function.
• To determine the molecular mechanisms underlying CO2-mediated regulation of Cx26 gap junctions.
• To explore the role of specific amino acid residues and pathological mutations in Cx26 CO2 responsiveness.

Main Methods:

• Dye transfer assays to assess gap junction permeability.
• Whole-cell recordings to measure gap junction conductance.
• Site-directed mutagenesis to investigate specific residues (K125, R104).
• Elastic network modeling to simulate protein dynamics.

Main Results:

• Elevated CO2 (55 mmHg) significantly reduced Cx26 gap junction conductance and delayed dye permeation.
• CO2-induced gap junction closure was dependent on residues K125 and R104, and independent of pH changes.
• Pathological Cx26 mutations abolished the CO2-dependent closure effect.
• CO2's effect on gap junctions is mechanistically distinct from its effect on hemichannels.

Conclusions:

• CO2 directly regulates Cx26 gap junction closure through a carbamylation-dependent mechanism involving K125 and R104.
• The functional consequences of CO2 on Cx26 gap junctions and hemichannels are opposing and depend on the protein's conformational state.
• Understanding CO2's role in Cx26 function is critical, especially in conditions involving altered CO2 levels or Cx26 mutations.