Acid-base regulation in exercising squid (Illex illecebrosus, Loligo pealei)

Squid (Illex illecebrosus, Loligo pealei) were cannulated in the vena cava and swum in a Beamish-type respirometer. Gas tensions and acid-base variables as well as octopine levels were estimated in samples of the mantle and of venous blood collected from quiescent, exercised, and recovered animals. When exhausted, both species exhibited a decrease in vena cava oxygen tensions and a slight alkalosis. With high swimming speeds prior to exhaustion in Illex a slight acidosis developed in the blood, which was linked to a severe intracellular acidosis. Generally, the drop in intracellular pH was linearly correlated with octopine accumulation in this species. Metabolic proton (and end-product) release from the mantle, however, was minimal, thus protecting arterial oxygen binding. High PCO2 values in the mantle of both species lead to the conclusion that the vena cava values analyzed in this and all literature studies on unrestrained cephalopods may not reflect the scope of respiratory acid-base changes in venous blood. Although metabolic changes in blood acid-base status are negligible, the respiratory acidification of venous mantle blood may allow for a classical function of Bohr and Haldane effects in these animals.