CO₂ per se activates carbon dioxide receptors

Area of Science:

• Molecular Biology
• Neuroscience
• Entomology

Background:

• Carbon dioxide (CO2) monitoring is crucial for mosquito population control.
• CO2 is detected by gustatory receptors (GRs) in mosquito maxillary palps.
• The exact chemical species (CO2 or bicarbonate) activating these receptors is unknown.

Purpose of the Study:

• To identify the specific chemical activator for mosquito CO2-sensing GRs.
• To determine the roles of different GR subunits (GR1, GR2, GR3) in CO2 detection.

Main Methods:

• Xenopus oocyte expression system used to study mosquito GR subunits (Culex quinquefasciatus, Aedes aegypti, Anopheles gambiae).
• Functional assays performed on oocytes coexpressing various combinations of GR subunits (GR1/3, GR1/2, GR2/3, GR1/2/3).
• Responses measured using sodium bicarbonate and varying concentrations of aqueous CO2.

Main Results:

• GR2 and GR3 subunits are essential for functional CO2 receptors.
• CO2-sensitive receptors showed robust responses to sodium bicarbonate, but significantly lower responses when GR1 was coexpressed.
• Direct correlation observed between dissolved CO2 concentration and receptor response, indicating CO2 is the direct activator.

Conclusions:

• Mosquito CO2-sensing gustatory receptors are primarily composed of GR2 and GR3 subunits.
• These receptors are directly activated by carbon dioxide (CO2) itself, not bicarbonate.
• GR1 appears to function as a modulator, influencing receptor sensitivity.