Ventilatory regulation of extracellular pH in crayfish exposed to changes in water titration alkalinity and NaCl...

The mechanisms of extracellular pH regulation were studied in normoxic crayfish Astacus leptodactylus during changes in water ionic composition at 13 degrees 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 decrease of water titration alkalinity, TAw, from 4 to 2 meq X L-1 simultaneously associated with either an increase of NaCl concentration, [NaCl]w, from 0.5 to 5 mmol X L-1, or a decrease of [NaCl]w, from 0.5 to 0.15 mmol X L-1. 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 compensation were observed. When [NaCl]w increased, the compensation was metabolic: the ventilatory requirement, VW X MO2-1, did not vary. When [NaCl]w decreased, the compensation was ventilatory: VW X MO2-1 doubled. It is concluded that in water-breathers ventilation, contrary to what is generally accepted, can play a role in extracellular ABB regulation.