The effects of saxitoxin and tetrodotoxin on nerve conduction in the presence of lithium ions and of magnesium ions.

1. It has been shown that nerve fibres from rat cauda equina will conduct action potentials after immersion in saline in which lithium chloride is substituted for sodium chloride.2. Both saxitoxin and tetrodotoxin inhibit lithium-generated action potentials. The concentration of toxin needed to inhibit the lithium-generated action potentials is similar to that needed to inhibit sodium-generated action potentials.3. If magnesium chloride is added to the saline to give a concentration of 10-15 mM there is usually a slight fall in amplitude of the compound action potential. Saxitoxin and tetrodotoxin now inhibit the action potential to a greater degree than in the absence of magnesium ions.