Extracellular and Intracellular Acid–Base Status in the Freshwater Crayfish Austropotamobius Pallipes Between 1 and 12 °C Available to Purchase

Freshwater crayfish, Austropotamobius pallipes, caught in the winter when water temperature was 5 °C, were acclimated in the laboratory to 5 °C for 1 week and to 1 and 12 °C for 1 month before haemolymph and tissue samples were taken for acid–base analysis. In vivo, haemolymph (extracellular) pH increased by 0.14 units between 5 and 1 °C but remained unchanged between 5 and 12 °C, giving an overall ΔpHe/Δt value of −0.009 pH units °C⁻¹ and an [H⁺] value of +3.3 nmol l⁻¹. Haemolymph withdrawn from crayfish acclimated to 1 °C and warmed anaerobically in vitro to 12 °C had a ΔpHe/Δt value of −0.010 pH units °C⁻¹. This was depressed compared with the values of −0.015 and −0.016 pH units °C⁻¹ obtained from haemolymph withdrawn from crayfish held at 5 and 12 °C, respectively, but changes in H⁺ concentration were similar in all three groups. There was little change in intracellular pH with rise in temperature in either claw muscle (ΔpHi/Δt= −0.003 pH units °C⁻¹) or hepatopancreas (ΔpHi/Δt= −0.006 pH units °C⁻¹). In the heart, ΔpHi/Δt paralleled that in the haemolymph (−0.010 pH units °C⁻¹), but the largest change was found in the abdominal muscle (−0.025 pH units °C⁻¹). In all tissues apart from claw muscle, there was a metabolic acidosis, with an increase in metabolic acid load as temperature rose from 1 to 12 °C. The depressed in vivo ΔpHe/Δt value and the differences in ΔpHi/Δt between the tissues were attributed to active regulation of pHi, possibly to control enzyme function in the intracellular compartments. Tissues that are functionally important in the winter months, such as abdominal muscle, followed alphastat regulation, whereas tissues that are less active in the winter, such as claw muscle and hepatopancreas, maintained pHi irrespective of temperature, resulting in a relatively acidotic pHi, which may serve to depress the activity of metabolic enzymes.