Mechanisms of carbon dioxide detection in the earthworm Dendrobaena veneta

• Published in: Frontiers in Ecology and Evolution
• Main Authors: Smith, Emily Jordan, Ryan, Jennifer L., Lopresti, Sofia A., Haghnazari, Dastan B. S., Anderson, Karleigh A. S., Lipson, Sarah J., Johnson, Erik C., Silver, Wayne L., Saunders, Cecil J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2023
• Subjects: Carbonic acid
• Online Access: http://dx.doi.org/10.3389/fevo.2023.1202410; https://www.frontiersin.org/articles/10.3389/fevo.2023.1202410/full

Introduction Carbon dioxide (CO 2 ) is a critical biological signal that is noxious to many animals at high concentrations. The earthworm Dendrobaena veneta lives in subterranean burrows containing high levels of CO 2 and respires through its skin. Despite the ecological and agricultural importance of earthworms, relatively little is known about how they make decisions in their environment, including their response to elevated levels of CO 2 . Methods To examine CO 2 detection in this species, we designed the exudate assay, in which we placed an earthworm in a sealed container, exposed it to varying concentrations of CO 2 for one minute, and recorded the amount of exudate secreted. Because earthworms excrete exudate in response to noxious stimuli, we hypothesized that the amount of exudate produced was proportional to the amount of irritation. We repeated these experiments after treatment with several blockers for molecules with potential involvement in CO 2 detection, including carbonic anhydrases, guanylate cyclase, TRPA1, ASICs, and OTOP channels. We also confirmed the presence of homologous transcripts for each of these gene families in an epithelial transcriptome for D. veneta . Additionally, since organisms often detect CO 2 levels indirectly by monitoring the conversion to carbonic acid (a weak acid), we used the exudate assay to evaluate aversion to additional weak acids (formic acid, acetic acid, and propionic acid). Results Earthworms excreted significantly more exudate in response to CO 2 in a dosage-dependent manner, and this response was muted by the general carbonic anhydrase inhibitor acetazolamide, the carbonic anhydrase IX/XII inhibitor indisulam, the calcium channel blocker ruthenium red, the sodium channel blocker amiloride, and the acid-sensing ion channel blocker diminazene aceturate. Discussion These data provide evidence of the role of carbonic anhydrase and epithelial sodium channels in earthworm CO 2 detection, establish that, similar to other subterranean-dwelling animals, earthworms ...