Heat Dissipation, Gas Exchange and Acid-Base Status in the Land Snail Oreohelix During Short-Term Estivation

Within 4 days following entry into estivation, heat dissipation and oxygen consumption by the land snail Oreohelix spp. decreased by 83% compared to standard non-estivating rates. During both non-estivating and estivating conditions, the quantity of heat dissipated per mole of O₂ consumed was indicative of a completely aerobic metabolism. This calorimetric-respirometric (C/R) ratio was −461±12 kJ mol⁻¹O₂ (S.E.M., N=5) under standard non-estivating conditions and −464±26 kJ mol⁻¹O₂ (N=4) during estivation. Respiratory exchange ratios reflected a primary dependence upon carbohydrate as a metabolic substrate during both states. Carbon dioxide retention occurred during the first 36h of estivation, resulting in an increase in hemolymph P_COCO2 and a decrease in pH. The respiratory acidosis during short-term estivation was not compensated by elevation of hemolymph [HCO₃⁻] above levels predicted from the in vitro nonbicarbonate buffer value of hemolymph. A brief period of rapid CO₂ release, which caused hemolymph P_COCO2 and pH to return to pre-estivation values, preceded the increase in O₂ consumption during arousal. Exposure of nonestivating snails to 4.67 kPa P_COCO2 (1 kPa=7.5 mmHg) caused a rapid and fully reversible 50% suppression of respiration rate. The temporal nature of CO₂ retention and release during entry into and arousal from estivation, and the suppression of O₂ consumption by artificial hypercapnia, support the hypothesis that elevated P_COCO2. or the resultant acidosis may contribute to metabolic suppression during estivation by land snails.