Dropping the base: recovery from extreme hypercarbia in the COtolerant Pacific hagfish (Eptatretus stoutii).

Abstract

Hagfish are capable of tolerating extreme hypercapnia (> 30 Torr) by mounting substantial plasma [HCO] (hypercarbia) to compensate for CO-mediated acidosis. The goal of this study was to characterize the mechanistic hypercarbia-recovery strategies in the highly COtolerant 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 [HCO] load (~ 70 mmol L) was rapidly offloaded. While increases in both whole-animal HCOexcretion and glomerular filtration were observed throughout recovery (2-8 h), neither can fully account for the observed rates of whole-animal HCOloss, which peaked at ~ 3.5 mmol kg h. Inhibition of carbonic anhydrase via acetazolamide revealed that the restoration of plasma [HCO] from hypercapnia-induced hypercarbia is likely facilitated in a dualistic manner, initially relying on both carbonic anhydrase mediated COoffloading and Cl/HCOexchange processes, both of which are likely either upregulated or further activated as recovery progresses.