Acid‐base balance and ion transfers in the spiny dogfish ( Squalus acanthias ) during hypercapnia: A role for ammonia excretion

• Published in: Journal of Experimental Zoology
• Main Authors: Claiborne, J. B., Evans, David H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1992
• Subjects: Animal Science and Zoology; General Medicine; spiny dogfish; Squalus acanthias
• Online Access: http://dx.doi.org/10.1002/jez.1402610103; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjez.1402610103; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jez.1402610103

Abstract The effect of hypercapnia on the acid‐base balance and acid‐equivalent transfers has been measured in the dogfish Squalus acanthias . Previous reports on Squalus are not in agreement as to the role played by compensatory acid‐base transfers between the animal and the water during hypercapnia. Cannulated animals were maintained in a closed circuit, seawater recirculation system. Plasma pH, Cco 2 (from which Pco 2 and [HCO 3 − ] were calculated), and transfers of NH 4 + and HCO 3 − ‐equivalent ions between the fish and the water, were measured during 24 hours of hypercapnic exposure (Pco 2 : 8–10 torr) and a subsequent 8–24 hour normocapnic recovery period. Respiratory acidosis resulted in a plasma pH depression, which was then almost completely compensated (within ˜ 0.1 pH unit) over 24 hours by a ˜ 20 mM increase in plasma [HCO 3 ]. In contrast to previous studies on elasmobranch acid‐base regulation, hypercapnia induced a rapid 3 × increase in not only HCO 3 − ‐equivalent uptake but also branchial ammonia (NH 4 + ) excretion. These transfers combined for a net Δ H + loss to the water of 5.5 mmol kg −1 . During the normocapnic period, net Δ H + was reversed to −6.9 mmol kg −1 , nearly completely due to HCO 3 ‐efflux. Several lines of evidence point to the contribution of gill Na + /NH 4 + exchange to the total ammonia excreted during hypercapnia, whereas NH 3 diffusion predominates during the recovery period. Likewise, Cl − /HCO 3 − or Cl − /OH − exchange may enhance the uptake of HCO 3 − during hypercapnia.