Connexin50 hemichannels are opened by CO₂: implications for lens physiology

Area of Science:

• Ophthalmology
• Cell Biology
• Biophysics

Background:

• Connexin50 (Cx50) is vital for lens function, as mutations cause cataracts.
• Cx50's role in the lens suggests a critical physiological function.
• A carbamylation motif in Cx50 hints at potential CO2 sensitivity.

Purpose of the Study:

• To investigate the CO2 sensitivity of Connexin50 (Cx50) hemichannels.
• To determine the role of the carbamylation motif in Cx50's CO2 response.
• To explore the physiological implications of Cx50 CO2 sensitivity in lens fiber cells.

Main Methods:

• Expressing full-length and truncated Cx50 in HeLa cells with genetically encoded sensors.
• Utilizing site-directed mutagenesis to probe the carbamylation motif (K105, K140) and cataract-associated mutations (V44).
• Performing Ca2+ imaging in lens slices and assessing NMDA receptor activation.

Main Results:

• Both full-length and truncated Cx50 hemichannels exhibit CO2-dependent opening.
• The carbamylation motif (K105, K140) is essential for Cx50's CO2 sensitivity.
• Cataract-associated mutations (V44) abolish Cx50 CO2 sensitivity.
• CO2-dependent Ca2+ influx occurs in lens fiber cells, partially mediated by NMDA receptors.

Conclusions:

• Cx50 hemichannels are directly gated by CO2, a novel mechanism for lens physiology.
• CO2-dependent Cx50 activity influences intracellular Ca2+ levels in lens fiber cells.
• This pathway may contribute to lens homeostasis through glutamate signaling and ion flux regulation.