Effect of Maintained Hypoxic Exposure on the Crayfish Orconectes Rusticus: Ii. Modulation of Haemocyanin Oxygen Affinity

Haemolymph Na+, Cl~, K+, Mg, Ca, Cu and protein levels, in vivo postbranchial acid-base status (total CO2, pH and PCOt), in vitro haemolymph buffer value, Bohr value and oxygen affinity were measured before and after a 31-week period in which control crayfish were maintained at normoxia and experimental crayfish were maintained at an ambient oxygen tension of 50-55 torr. Analysis of haemolymph Cu and protein levels in control and experimental crayfish indicated no increase in haemocyanin and therefore oxygen carrying capacity of the haemolymph. Although the Bohr value was not significantly different between control and experimental crayfish, the haemocyanin oxygen affinity was elevated in the hypoxic crayfish by two mechanisms. The first was dependent upon the haemolymph H+ concentration, i.e. a Bohr shift resulting from a respiratory alkalosis. The second mechanism was independent of haemolymph H concentration in that at a given pH haemolymph from experimental crayfish had a significantly higher oxygen affinity. The decrease in /^probably cannot be attributed to a specific cation effect.