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_i) despite large reductions in extracellular (blood) pH (pH_e), termed preferential pH_i regulation, in response to elevated environmental PCO₂ (hypercarbia) and in general appear to be relatively resilient to stressors. Preferential pH_i regulation is thought to be associated with hypercarbia tolerance in general, but has also recently been observed to protect pH_i against metabolic acidoses induced by exhaustive exercise and anoxia in a tropical air breathing catfish. We hypothesized that preferential pH_i regulation may also be a general strategy of acid-base regulation in sturgeon. To address this hypothesis, severe acidoses were imposed to reduce pH_e, and the presence or absence of preferential pH_i 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_e 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_i. Following hyperoxia, heart, brain and liver pH_i were preferentially regulated against the reduction in pH_e, similar to hypercarbia exposure. Following all metabolic acidoses heart pH_i was protected and brain pH_i remained unchanged following exhaustive exercise and air exposure, however, brain pH_i was reduced following anoxia. Liver and white muscle pH_i were reduced following all metabolic acidoses. These results suggest preferential pH_i regulation may be a general strategy during respiratory acidoses but during metabolic acidoses, the response differs between source of acidoses and tissues.