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This Article Full Text Full Text (PDF) All Versions of this Article: 296/6/R1868    most recent 90767.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Google Scholar Articles by Baker, D. W. Articles by Brauner, C. J. PubMed PubMed Citation Articles by Baker, D. W. Articles by Brauner, C. J.

ENVIRONMENTAL PHYSIOLOGY

Complete intracellular pH protection during extracellular pH depression is associated with hypercarbia tolerance in white sturgeon, Acipenser transmontanus

¹Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada; ²Department of Biology, San Diego State University, San Diego, California; ³Center for Marine and Environmental Research (CIIMAR), Porto, Portugal; and ⁴Faculty of Science and Technology, Vancouver Island University, Nanaimo, British Columbia, Canada

Submitted 12 September 2008 ; accepted in final form 29 March 2009

Sturgeons are among the most CO₂ tolerant of fishes investigated to date. However, the basis of this exceptional CO₂ tolerance is unknown. Here, white sturgeon, Acipenser transmontanus, were exposed to elevated CO₂ to investigate the mechanisms associated with short-term hypercarbia tolerance. During exposure to 1.5 kPa PCO₂, transient blood pH [extracellular pH (pHe)] depression was compensated within 24 h and associated with net plasma HCO₃^– accumulation and equimolar Cl^– loss, and changes in gill morphology, such as a decrease in apical surface area of mitochondrial-rich cells. These findings indicate that pHe recovery at this level of hypercarbia is accomplished in a manner similar to most freshwater teleost species studied to date, although branchial mechanisms involved may differ. White sturgeon exposed to more severe hypercarbia (3 and 6 kPa PCO₂) for 48 h exhibited incomplete pH compensation in blood and red blood cells. Despite pHe depression, intracellular pH (pHi) of white muscle, heart, brain, and liver did not decrease during a transient (6 h of 1.5 kPa PCO₂) or prolonged (48 h at 3 and 6 kPa PCO₂) blood acidosis. This pHi protection was not due to high intrinsic buffering in tissues. Such tight active cellular regulation of pHi in the absence of pHe compensation represents a unique pattern for non-air-breathing fishes, and we hypothesize that it is the basis for the exceptional CO₂ tolerance of white sturgeon and, likely, other CO₂ tolerant fishes. Further research to elucidate the specific mechanisms responsible for this tremendous pH regulatory capacity in tissues of white sturgeon is warranted.

sturgeon; acid-base regulation; intracellular pH; CO₂ tolerance; hypercarbia/hypercapnia