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Journal of Experimental Biology 138,289-299 (1988)
Published by Company of Biologists 1988

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

M. CHRISTOPHER BARNHART ¹ and BRIAN R. McMAHON ¹

¹ Department of Biology, University of Calgary Calgary, Alberta T2N 1N4, Canada

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 (V_O2) and on extracellular and intracellular pH of active (i.e. non-dormant) individuals. Active snails reduced V_O2, by 50% within l h when exposed to 65mmHg (1 mmHg = 133.3Pa) ambient P_CO2, and by 63% in 98mmHg. These levels of CO₂ are within the range that occurs naturally in the lung and blood during dormancy. V_O2 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 P_CO2 by approximately 0.7logP_CO2 Critical (V_O2- limiting) ambient P_O2 of active snails was 90mmHg in the absence of CO₂ and dropped to 50 mmHg when V_O2 was reduced 45% by exposure to CO₂. Estimated critical P_O2 at the lower V_O2 typical of dormancy is well below the typical lung P_O2 of dormant Otala, suggesting that P_O2 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 V_O2 by hypoxia.

Note:

Present address: Physiological Research Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.

Key words: Pulmonata, Helicidae, dormancy, metabolic arrest, intracellular pH, hypercapnia, hypoxia

Accepted on April 7, 1988

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