Springer Online Journal Archives 1860-2000
Summary At the onset of moderate swimming activity,Callinectes sapidus rapidly increased branchial ventilation, heart rate, and oxygen uptake, reaching steady state values in 2–3 min, with a half-time of 30 sec. Although O2 extraction efficiency decreased slightly (50% to 43%) upon reaching steady state, O2 uptake was increased 2.6 fold over resting (routine) levels. HemolymphP O 2 did not change during sustained (30–60 min) exercise, but a marked decrease in pH (7.60 to 7.10), associated with a 14-fold increase in hemolymph lactate concentration, caused decreases in both pre-and postbranchial O2 content due to a large hemocyanin Bohr shift. The effect of the Bohr shift on O2 binding, however, was minimized by an increase in hemocyanin O2 affinity induced by lactate ions; the influence of lactate on hemocyaninP 50 was shown to be the same in vivo and in vitro. As a result of the interaction between the Bohr and lactate effects, only slight increases were observed in the a-v O2 difference (13%) and the quantitative role of hemocyanin in oxygen transport (11%) during exercise. The increase in O2 delivery was therefore attributed primarily to a 2.3 fold increase in cardiac output (Fick estimate), resulting from increases in both heart rate (1.61 X) and stroke volume (1.42X). During exercise hemocyanin remained 21% oxygenated upon leaving the tissues, thus maintaining a substantial ‘venous O2 reserve’ which could be utilized to fuel more strenuous levels of exercise at least partly by aerobic pathways. The high hemolymph lactate levels, however, indicate that anaerobic metabolism makes a significant contribution to energy production even during moderate exercise. These results are similar to the respiratory and circulatory responses reported for other decapod crustaceans and fish during mild exercise.C. sapidus, however, appears to be highly resistant to fatigue, which correlates with its welldeveloped locomotor capabilities.
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