Integrated Function of the Respiratory Pigment Hemocyanin in Crabs

A large number of factors are now known to influence the oxygen affinity of hemocyanins in crabs. In this article I review several case studies in which a number of different variables, including pH, CO2, calcium ions, lactate, urate, dopamine, and temperature, act together on hemocyanin oxygen affinity to bring about adaptive changes in oxygen transport. These changes act in tandem with ventilatory and cardiovascular adjustments to stabilize oxygen uptake during hypoxia or to increase oxygen uptake during exercise in a swimming crab. It is important, however, that the effects of the different modulators be examined at very low concentrations, where their effects are large, to assess their importance in resting crabs where their concentrations may be low. Temperature effects among hemocyanins in crabs are variable and the magnitude may be inversely related to the magnitude of the Bohr effect. Several examples are presented of acclimation effects where oxygen affinity increases significantly at cold temperatures. The acclimation response may be important in partially regulating the metabolic responses of crabs to seasonal changes in temperature.