Metabolic changes associated with acid-base regulation during hypercarbia in the CO2-tolerant chondrostean, white sturgeon (Acipenser transmontanus)

CO2 tolerance in white sturgeon is associated with the ability to tightly regulate intracellular pH (pHi) despite a large reduction in extracellular pH (pHe) termed preferential pHi regulation. How this regulatory response affects whole animal metabolic rate is unknown. Accordingly, we characterized oxygen consumption rate (<(M)over dot>(O2)) and metabolically-relevant organismal and cellular responses in white sturgeon during exposure to hypercarbia. White sturgeon were able to protect intracellular pH (pHi) in liver and white muscle as early as 6 h (the earliest time period investigated) following exposure to severe (sub-lethal) hypercarbia (45 and 90 mmHg PCO2). Sturgeon exposed to 15 and 30 mmHg PCO2 exhibited pHe compensation and significant increases in M-O2 (up to 80% greater than control values). In contrast severe hypercarbia (>= 45 mmHg PCO2) elicited an uncompensated reduction in pHe (up to similar to 1.0 pH units) and red blood cells (as great as similar to 0.5 pH units), and was accompanied by 30 and 60% reductions in <(M)over dot>(O2), respectively. While behavioral, respiratory and cellular responses to hypercarbia were observed, none corresponded well with the pattern or magnitude of changes in <(M)over dot>(O2). The findings of this research provide empirical support for the hypothesis that preferential pHi regulation is not metabolically costly, and thus may have been a strategy strongly selected for in fishes encountering short-term hypercarbia. (C) 2011 Elsevier Inc. All rights reserved.