Mechanisms of acid-base excretion across the gills of a marine fish

✍ Scribed by Claiborne, James B.; Perry, Erin; Bellows, Shenna; Campbell, Jennifer

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 299 KB
• Volume: 279
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/(sici)1097-010x(19971201)279:5<509::aid-jez15>3.0.co;2-2

✦ Synopsis

Na + /H + and Cl -/HCO 3 -exchanges in the branchial epithelium are thought to be primarily responsible for acid-base transfers in fish. Several different cellular mechanisms have been proposed to drive these exchanges in fresh water and marine species. We measured the acidbase balance and net H + transfers (∆H + ) in the marine long-horned sculpin (Myoxocephalus octodecimspinosus) following acidosis. ∆H + was determined in different groups of acid loaded (2-3 meq kg -1 ) animals which were: 1) adapted to seawater (SW); 2) adapted to 20% SW; 3) exposed to water with artificially low [Na + ] or [Cl -]; 4) exposed to water containing 1 × 10 -4 M amiloride, 5-(N,N-hexamethylene)-amiloride (HMA), or 4,4´-diisothiocyanatostilbene-2,2´-disulfonic acid (DIDS). Both seawater and 20% SW adapted fish were able to completely compensate for the infused load and over 24 hours typically over-excreted more than 2× the amount infused. A 30% decrease in plasma P CO2 following the metabolic acidosis in sculpin adpated to 20% SW (presumably secondary to respiratory alterations) contributed to the rapid recovery of blood pH. Low ambient [Na + ] reversed normal acid excretion to an uptake (HCO 3 -loss; even after acid infusion). 20-30 mM Na + in the water was necessary to induce a positive ∆H + . A reversible inhibition of ∆H + was also observed in sculpin exposed to either amiloride or HMA during the acidosis. In contrast, low [Cl -] or DIDS enhanced ∆H + excretion. We conclude that net H + excretion measured following acidosis in these seawater or brackish water adapted animals is the sum of parallel (and counter acting) apical gill Na + /H + and Cl -/HCO 3 -exchanges. The Na + /H + transfers are most likely via an antiporter of the NHE family and occur on the background of continued "band-3" Cl -/HCO 3 -exchange.