Depression of Aerobic Metabolism and Intracellular pH by Hypercapnia in Land Snails, Otala Lactea

The pulmonate land snail Otala lactea undergoes simultaneous hypercapnia, hypoxia, extracellular acidosis and metabolic depression during dormancy. We tested the effects of ambient hypercapnia and hypoxia on oxygen consumption and on extracellular and intracellular pH of active (i.e. non-dormant) individuals. Active snails reduced by 50% within 1h when exposed to 65 mmHg (1 mmHg = 133·3 Pa) ambient and by 63% in 98 mmHg. These levels of CO₂ are within the range that occurs naturally in the lung and blood during dormancy. of hypercapnic snails remained below that of controls for the duration of exposure (up to 9 h) and returned to control levels within 1 h when CO₂ was removed. Both pHe and whole-body pHi (measured using [¹⁴C]DMO) fell with increasing haemolymph by approximately 0·71og⁠. Critical ( -limiting) ambient of active snails was 90 mmHg in the absence of CO₂ and dropped to 50 mmHg when was reduced 45% by exposure to CO₂. Estimated critical at the lower typical of dormancy is well below the typical lung of dormant Otala, suggesting that in the lung does not normally limit oxygen consumption during dormancy. These results support the hypothesis that hypercapnia or resulting respiratory acidosis depresses metabolic rate during dormancy, and argue against a limitation of by hypoxia.