Oxygen transport in Crayfish blood: Effect of thermal acclimation, and short-term fluctuations related to ventilation and cardiac performance
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ThepO2 in the hemolymph of the decapod crustaceanAstacus leptodactylus was measured continuously with micro O2 electrodes. PostbranchialpO2, heart rate and ventilation rate were simultaneously recorded. PrebranchialpO2 was measured in a separate series of experiments. Crayfish acclimated for six weeks to warm (20 °C) and cold (10 °C) conditions were studied.
Postbranchial bloodpO2 was measured in the pericardium. Typical values for warm-acclimated animals fell in the range 23–35 Torr, with a mean of 28.3 Torr, and those for cold-acclimated animals were 17–30 Torr, with a mean of 24.4 Torr. PrebranchialpO2 was measured in the meropodites of the 8th thoracopod. VenouspO2 levels ranged from 7–13 Torr, mean 9.4 Torr (warm-acclimated), and 6–9 Torr, mean 6.8 Torr (cold-acclimated).
pO2 values of resting, restrained animals were variable and fluctuations occurred in both the pre- and the postbranchial levels. Fluctuations were either small (1–5 Torr) or large (10–70 Torr).
PostbranchialpO2 correlated with fluctuations in the ventilation and heart rates. ArterialpO2 rose when the ventilation rate was increased, with a delay of about 10 s in warm-acclimated and 20 s in cold-acclimated animals, respectively. Along with increasingpaO2 an increase of the heart rate was established.
In resting animals, there is no a-v pH-difference. Cell-free hemolymph, taken from the pericardium or the meropodites, had a pH of 7.48 or 7.47, respectively, in warm-acclimated animals and 7.94 or 7.97 in cold-acclimated animals. Under these conditions the hemocyanin was 99% saturated in the artial blood and 45% in venous (warm-acclimated). Corresponding values in cold-acclimated crayfish were 98% and 61%, respectively.
TheP50 of the hemocyanin in undiluted hemolymph was 10 Torr at 20 °C and pH 7.42, and 6.2 Torr at 10 °C and pH 7.92. The hemocyanin showed a weak Bohr effect (ΔlogP50/ΔpH=−0.19 in warm-acclimated, and −0.20 in cold-acclimated animals). The pH range of the Bohr effect fell into the in vivo pH range in each group and thus differed by 0.5 pH units between the two groups.
KeywordsOxygen Heart Rate Human Physiology Oxygen Transport Ventilation Rate
oxygen tension of postbranchial (arterial) blood
oxygen tension of prebranchial (venous) blood
%O2 saturation of postbranchial blood
%O2 saturation of prebranchial blood
pO2 at half saturation of hemocyanin
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