The effects of external acidification on the ionic composition of the haemolymph, acid-base balance and sodium metabolism in the pulmonate freshwater snail, Lymnaea stagnalis

1. 1. In L. stagnalis exposed to external pHs below 4.5 the haemolymph Na + and Cl − concentrations decreased. Acid-base balance became affected at still lower pHs. 2. 2. In exposition experiments acidification of the ambient medium decreased the Na + influx and increased the Na + efflux. The latter effect was apparent below pH 6.0. 3. 3. In adaptation experiments under steady state conditions, the Na + influx ( = Na + turnover rate) increased when the external pH decreased. Also this effect was apparent from pH 6.0. 4. 4. The deteriorating effects of acidification increased with decreasing external Na + and Cl − concentrations. They were independent of the external Ca 2+ concentration. 5. 5. Renal Na + losses decreased under acid conditions. The increment in the Na + efflux, therefore, must be due to integumental losses.