Is the resting rate of oxygen consumption of locomotor muscles in crustaceans limited by the low blood oxygenation strategy?

Abstract

Numerous water-breathers exhibit a gas-exchange regulation strategy that maintains O2 partial pressure, PO2, in the arterial blood within the range 1-3 kPa at rest during the daytime. In a night-active crustacean, we examined whether this could limit the rate of O2 consumption (ṀO2) of locomotor muscles and/or the whole body as part of a coordinated response to energy conservation. In the crayfish Astacus leptodactylus, we compared the in vitro relationship between the ṀO2 of locomotor muscles as a function of the extracellular PO2 and PCO2 and in vivo circadian changes in blood gas tensions at various values of water PO2. In vitro, the ṀO2 of locomotor muscle, either at rest or when stimulated with CCCP, was O2-dependent up to an extracellular PO2 of 8-10 kPa. In vivo, the existence of a night-time increase in arterial PO2 of up to 4kPa at water PO2 values of 20 and 40 kPa was demonstrated, but an experimental increase in arterial PO2 during the day did not lead to any rise in whole-body ṀO2. This suggested that the low blood PO2 in normoxia has no global limiting effect on daytime whole-body ṀO2. The participation of blood O2 status in shaping the circadian behaviour of crayfish is discussed.