Effect of Ions on the Efflux of Acetylcholine from Peripheral Nerve

The nerves from the walking leg of lobster released acetylcholine (ACh) even when the ends were tied off, although this release was significantly increased when the nerve endings were not tied. The resting nerves were kept in sea water containing physostigmine. In absence of physostigmine no ACh was found in the surrounding fluid. Removal of Ca from the sea water reduced the release of ACh, while increased concentrations of Ca had no significant effect. Removal of Mg⁺⁺ or increased Mg⁺⁺ concentrations in the presence of normal Ca⁺⁺ concentrations increased the release of ACh. Increased K⁺ concentrations had a stimulating action on the efflux of ACh. Increased or reduced Na⁺ concentrations had only slight effects on the release of ACh in resting lobster nerve. During the 4 hr observation period the excised nerves were still able to synthesize ACh. The choline acetylase activity was stimulated by increased concentrations of Mg⁺⁺ and K⁺. The effects of ions on the release of ACh are similar to those reported at the junction.