Abstract
The mechanisms of extracellular pH regulation were studied in normoxic crayfish Astacus leptodactylus during changes in water ionic composition at 13°C. In artificial waters all ambient physico-chemical properties were controlled. Ventilatory changes and the time course of hemolymph acid-base balance, ABB, were followed after a decrase of water titration alkalinity, TAw, from 4 to 2 meq·L − simultaneously associated with either an increase of NaCl concentration. [NaCl]w, from 0.5 to 5 mmol·L −, or a decrease of [NaCl]w, from 0.5 to 0.15 mmol·L −. The ABB changes were characterized by a hypercapnic acidosis attributable to the decrease of TAw. Depending on the simultaneous change of [NaCl]w, two different mechanisms of compensations were observed. When [NaCl] increased, the compensation was metabolic: the ventilatory requirement, V̇ w·Ṁ O 2 −, did not vary. When [NaCl]w decreased, the compensation was ventilatory: V̇ w·Ṁ O 2 − doubled. It is concluded that in water-breathers ventilation, contrary to what is generally accepted, can play a role in extracellular ABB regulation.
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