In Vivo Analysis of Gas Transport in Arterial and Venous Blood of the Sea Lamprey Petromyzon Marinus

Exercise in sea lampreys resulted in a significant decrease in the extracellular pH (pHe) in both arterial and venous blood. At rest, the erythrocyte pH (pHi) of venous blood was significantly greater than the pHi of arterial blood. Despite the considerable extracellular acidosis after exercise, both arterial and venous pHi were maintained throughout the recovery period. In the venous blood, there was a reversal of the pH gradient (ΔpH) across the erythrocyte membrane immediately after exercise. Exercise also resulted in significant reductions in the partial pressure of oxygen and hemoglobin oxygen-carriage and a significant increase in the partial pressure of CO₂ in arterial and venous blood. Although the total CO₂ concentration of the plasma decreased after exercise, erythrocyte total CO₂ concentrations (C_COCO2,i) increased. In venous blood, the C_COCO2,i immediately after exercise was double the resting value. At rest, partitioning of the total CO₂ content between plasma and erythrocytes indicated that 16 % and 22 % of the total CO₂ could be attributed to the erythrocytes in arterial and venous whole blood, respectively. After exercise, these percentages increased to 25% (arterial) and 38% (venous). Changes in C_COCO2,i accounted for 62% of the arteriovenous difference in whole-blood total CO₂ at rest. This increased to 78% immediately after exercise. Thus, unlike other vertebrates, CO₂ transport in the lamprey in vivo is largely dependent on erythrocyte CO₂-carriage.