The importance of carbonic anhydrase II in red blood cells during exposure of chicken embryos to CO₂

The importance of carbonic anhydrase (CA) during exposure of chicken embryos to CO₂ during the second half of incubation was investigated. The protein abundance and activity of CAII in erythrocytes was significantly higher in CO₂-exposed embryos compared to normal conditions. Daily injections of acetazolamide (ATZ), an inhibitor of CA, increased blood PCO2 and decreased blood pH in both control and CO₂-incubated embryos. ATZ increased blood bicarbonate concentration in embryos exposed to normal atmosphere and in day-12 embryos exposed to high CO₂. The tendency of an increased blood potassium concentration in ATZ-injected embryos under standard atmospheric conditions might indicate that protons were exchanged with intracellular potassium. However, there was no evidence for such an exchange in CO₂-incubated ATZ-treated embryos. This study shows for the first time that chicken embryos adapt to CO₂ during the second half of incubation by increasing CAII protein expression and function in red blood cells. This response may serve to " buffer" elevated CO₂ levels.