Carbon dioxide and bicarbonate accumulation in caiman erythrocytes during diving

The ability of crocodilian haemoglobins to bind HCO₃ ^- has been appreciated for more than half a century, but the functional implication of this is exceptional mechanism has not previously been assessed in vivo Therefore, the goal of the present study was to address the hypothesis that CO₂ primarily binds to Hb, rather than being accumulated in plasma as in other vertebrates, during diving in caimans. Here, we demonstrate that CO₂ primarily accumulates within the erythrocyte during diving and that most of the accumulated CO₂ is bound to haemoglobin. Furthermore, we show that this HCO₃ ^--binding is tightly associated with the progressive blood deoxygenation during diving, therefore, crocodilians differ from the classic vertebrate pattern, where HCO₃ ^- accumulates in the plasma upon excretion from the erythrocytes by the Cl^--HCO₃ ^--exchanger.