Physiological Responses of the Crayfish<i>Pacifastacus leniusculus</i>(Dana) to Environmental Hyperoxia. III. Intracellular Acid-Base Balance

Abstract

The 14C-DMO/3H-inulin technique was used to measure tissue intracellular (IC) pH (pHi) in the crayfish Pacifastacus leniusculus in normoxic fresh water at 12° C, after 72 h hyperoxia (O₂ tension [Po2] = 500 mmHg; 1 mmHg = 133.3 Pa) and subsequent recovery. The tissues examined were abdominal and claw muscle, heart muscle, nerve, antennal gland, and carapace. Soft tissues had a control pHi that was acid relative to extracellular (EC, hemolymph) pH (pHe). The pHe-pHi gradient varied from 0.1 pH units in nerve and antennal gland to between 0.2 and 0.5 pH units in cardiac and skeletal muscle; pHi in carapace meanwhile was 0.3 pH units more alkaline than pHe. Intracellular nonbicarbonate buffering capacity (β) was equivalent in claw muscle, antennal gland, heart muscle, and cellular hypodermis (-20 mmol · pH unit⁻¹ · L⁻¹). Values were higher in abdominal muscle and highest in nerve. The initial extracellular response to hyperoxia was a hypercapnic acidosis of about 0.3 pH units that was compensated within 48 h by metabolic [HCO₃⁻ + CO₃²⁻] accumulation. On recovery circulating [HCO₃⁻ + CO₃²⁻] levels were rapidly restored. Acid-base balance in soft tissues followed a similar trend. The initial acidosis varied from 0.2 pH units in nerve and heart to 0.5 pH units in skeletal muscle and antennal gland; this was largely of metabolic origin in skeletal muscle, of mixed origin in antennal gland and nerve, and primarily of respiratory origin in heart. In all tissues except heart, the acidosis was subsequently compensated by metabolic IC [HCO₃⁻ + CO₃²⁻] accumulation. Control IC [HCO₃⁻ + CO₃²⁻] levels were rapidly reestablished during recovery in all tissues except heart and nerve. Carapace similarly experienced an initial acidosis that accommodated with hyperoxic exposure although pHi was not entirely corrected. On recovery carapace exhibited a metabolic alkalosis that was the opposite of changes observed in soft tissues. Changes in the IC acidic equivalent pool measured in this study agreed with values predicted in an earlier whole-animal flux study, which confirmed that the IC compartment contributes around 75% of the H⁺ excreted by the crayfish into the experimental water during hyperoxia.