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 CO 2 in arterial and venous blood. Although the total CO 2 concentration of the plasma decreased after exercise, erythrocyte total CO 2 concentrations ( C CO CO2 ,i ) increased. In venous blood, the C CO CO2 ,i immediately after exercise was double the resting value. At rest, partitioning of the total CO 2 content between plasma and erythrocytes indicated that 16 % and 22 % of the total CO 2 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 CO CO2 ,i accounted for 62% of the arteriovenous difference in whole-blood total CO 2 at rest. This increased to 78% immediately after exercise. Thus, unlike other vertebrates, CO 2 transport in the lamprey in vivo is largely dependent on erythrocyte CO 2 -carriage.