Control of acid-base status in active and dormant land snails,Otala lactea (Pulmonata, Helicidae)

Abstract

Control of extracellular acid-base status was examined during activity and dormancy inOtala lactea (Pulmonata, Helicidae). Active snails showed little variation in hemolymph pH and $$P_{CO_2 } $$ at constant temperature. With increase of temperature, hemolymph $$P_{CO_2 } $$ increased from about 6 Torr at 5°C to 13 Torr at 24°C and pH decreased by about 0.017 pH units/°C, a pattern consistent with alphastat regulation of pH via ventilatory control of $$P_{CO_2 } $$ . During dormancy, mean hemolymph $$P_{CO_2 } $$ increased to about 50 Torr. Venous pH declined by about 0.4 units due to hypercapnia and fluctuated more widely than in active snails due to variability of $$P_{CO_2 } $$ . Hemolymph pH declined further in prolonged dormancy due to progressive metabolic acidosis; after one year of dormancy the mean hemolymph pH was about 0.8 units lower than that of active snails at similar temperature. Active snails exposed experimentally to high $$P_{CO_2 } $$ showed a large increase in hemolymph [HCO 3 − ]. However, [HCO 3 − ] declined by up to 50% during dormancy, despite the naturally occurring hypercapnia. Hemolymph osmolality and the concentrations of solutes other than [HCO 3 − ] increased with increasing duration of dormancy. Concentrations of magnesium and calcium increased about 2.5 times more rapidly than those of sodium and chloride, indicating that acidosis is partially offset by the dissolution of carbonates from the shell or tissues.