Respiratory properties of erythrocruorin (Extracellular hemoglobin) in the blood of the annelidArenicola marinawith special reference to the influences of salinity and temperature

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Abstract
Acclimation of Arenicola marina to high salinity increases the O2 affinity of the etythrocruorin in the blood compared to that in low-salinity acclimated animals; at pH 7.4 and 20°C, the O2 tensions required for half-saruration (P50) are 2.1 and 3.3 mm Hg at water salinities of 32.3 and 10.2 ‰, respectively. Acclimation salinity, however, does not appear to e~ert a consistent influence on the Bohr effect (Δlog P50/ΔpH) or the buffer capacity of the blood, although the buffer reserve is higher in low- than in high-salinity acclimated animals. The influence of temperature on the O2 affinity of the blood is small (the apparent heat of oxygenation approximates -5 to -6 kcal · mole-1, compared to -10 to -14 kcal · mole-1 in vertebrate hemoglobin) and appears to be independent of salinity. Acclimating batches of Arenicola to 6 and 18°C, however, produced no evidence for thermo-acclimatory changes in blood O2 affinity. Curiously a specific effect of CO2 (i.e. one which is not related to concomitant pH change) increases O2 affinity of the erythrocruorin rather than decreasing it as in vertebrate hemoglobin. The data are discussed as regards their possible adaptive significance to the worms in burrowing and intertidal habitats.