1. Substitution by different anions for chloride in physiological salt solutions leads to binding between Ca²⁺ and the anion. Experiments designed to test effects of Cl^- therefore often show mixed effects of changes in Cl^- and Ca²⁺ activity.

 

2. This mixed effect is demonstrated in neurons of the snail, Helix pomatia: current-voltage characteristics and membrane potential are described during reduction of extracellular Cl^- using different anions as substitutes. Methylsulphate is concluded to be the best substitute in this preparation.

3. The association constants for the binding of Ca²⁺ to a number of anions is given.