Temperature-induced variations of blood acid-base status in the lugworm, Arenicola marina (L.): II. In vivo study.

Lugworms, Arenicola marina (L.), acclimatized at 16-17 degrees C, were acclimated at temperatures between 5.3 and 25.7 degrees C for 96 h. Whereas in vitro Arenicola blood behaves like a Rosenthal system, in vivo prebranchial blood does not: the higher the acclimation temperature, the lower the pHv and [HCO3]V, PVCO2, remaining practically constant. Nevertheless, the very low relative alkalinity of the blood in vivo ([OH-]/[H+] is less than 3), and the degree of dissociation of extra- and intracellular proteins, remain practically constant whatever the temperature. From examples in the literature together with these results, it is concluded that poikilothermic air-breathers and poikilothermic water-breathers regulate their blood pH in the face of temperature changes by contrasting mechanisms. In the first, regulation is almost instantaneous and takes place at the pulmonary level through adjustment of CO2 exchanges. In the second this regulation is slow and mainly extraventilatory, occurring through ionic exchanges. This contrast must be considered in relation with differences in blood PCO2 values, caused by the much higher O2 capacitance of air compared to water.