Relationships between apparent net H+ excretion and Na+, Ca2+ and Cl− uptake in the pulmonate freshwater snail Lymnaea stagnalis

Abstract 1. 1. Lymnaea stagnalis was able to take up Na + from Cl − -free (1 mM Na + ) and Cl − from Na + -free (1 mM Cl − ) media. The respective uptake rates, however, were smaller than those from 1 mM NaCl. 2. 2. Under Cl − -free conditions Na + uptake coincided with almost equivalent apparent net H + excretion. 3. 3. Cl − uptake under Na + -free conditions did not coincide with negative apparent net H + excretion, but with equivalent net Ca 2+ uptake. 4. 4. Under NaCl-free conditions the snails continuously absorbed Ca 2+ associated with equivalent apparent net H + excretion. 5. 5. The model for the mechanisms of Na + and Cl − uptake in L. stagnalis , by Na + /H + and Cl − /HCO 3 − exchange, have to be extended with Ca 2+ /2H + exchange and/or Ca 2+ −2HCO 3 − cotransport.