White sturgeon (Acipenser transmontanus) acid-base regulation differs in response to different types of acidoses.

White sturgeon (Acipenser transmontanus) completely protect intracellular tissue pH (pH) despite large reductions in extracellular (blood) pH (pH), termed preferential pH regulation, in response to elevated environmental PCO (hypercarbia) and in general appear to be relatively resilient to stressors. Preferential pH regulation is thought to be associated with hypercarbia tolerance in general, but has also recently been observed to protect pH against metabolic acidoses induced by exhaustive exercise and anoxia in a tropical air breathing catfish. We hypothesized that preferential pH regulation may also be a general strategy of acid-base regulation in sturgeon. To address this hypothesis, severe acidoses were imposed to reduce pH, and the presence or absence of preferential pH regulation was assessed in red blood cells (RBC), heart, brain, liver and white muscle. A respiratory acidosis was imposed using hyperoxia, while metabolic acidoses were induced by exhaustive exercise, anoxia or air exposure. Reductions in pH occurred following hyperoxia (0.15 units), exhaustive exercise (0.30 units), anoxia (0.10 units) and air exposure (0.35 units); all acidoses reduced RBC pH. Following hyperoxia, heart, brain and liver pH were preferentially regulated against the reduction in pH, similar to hypercarbia exposure. Following all metabolic acidoses heart pH was protected and brain pH remained unchanged following exhaustive exercise and air exposure, however, brain pH was reduced following anoxia. Liver and white muscle pH were reduced following all metabolic acidoses. These results suggest preferential pH regulation may be a general strategy during respiratory acidoses but during metabolic acidoses, the response differs between source of acidoses and tissues.