Hagfish are capable of tolerating extreme hypercapnia (> 30 Torr) by mounting substantial plasma [HCO3−] (hypercarbia) to compensate for CO2-mediated acidosis. The goal of this study was to characterize the mechanistic hypercarbia-recovery strategies in the highly CO2 tolerant hagfish. We exposed hagfish to hypercapnia (30 Torr) for 48 h and allowed a 24 h recovery period in normocapnic seawater. Within 8 h of the recovery period, the compensatory plasma [HCO3−] load (~ 70 mmol L−1) was rapidly offloaded. While increases in both whole-animal HCO3− excretion and glomerular filtration were observed throughout recovery (2–8 h), neither can fully account for the observed rates of whole-animal HCO3− loss, which peaked at ~ 3.5 mmol kg−1 h−1. Inhibition of carbonic anhydrase via acetazolamide revealed that the restoration of plasma [HCO3−] from hypercapnia-induced hypercarbia is likely facilitated in a dualistic manner, initially relying on both carbonic anhydrase mediated CO2 offloading and Cl−/HCO3− exchange processes, both of which are likely either upregulated or further activated as recovery progresses.
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We thank Dr. Eric Clellend for his unwavering diligence in supporting this research, the BMSC Foreshore staff for their aid in obtaining research animals and Dr. Chris Wood for experimental advice.
A.M.C. was supported by an NSERC- PGSD, Alberta Innovates Technology Futures—Omics Scholarship, President’s Doctoral Prize of Distinction, Donald M. Ross Memorial Scholarship, R. E. (Dick) Peter Memorial Scholarship, Andrew Stewart Memorial Prize, Western Canadian Universities Marine Sciences Society Graduate Student Award and the Dick and Leona Peter BMSC residential bursary. A.M.W was supported by a NSERC-PGSD, The Presidents Doctoral Prize of Distinction, Queen Elizabeth II Scholarship, Sigurd Tviet Memorial Scholarship, Dick and Leona Peter BMSC Residential bursary and the John Boom Scholarship. This research was supported by an NSERC Discovery Grant (203736) to GGG.
Communicated by I.D. Hume.
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Clifford, A.M., Weinrauch, A.M. & Goss, G.G. Dropping the base: recovery from extreme hypercarbia in the CO2 tolerant Pacific hagfish (Eptatretus stoutii). J Comp Physiol B 188, 421–435 (2018). https://doi.org/10.1007/s00360-017-1141-2
- Carbonic anhydrase