The ionic regulation of action potentials in the axon of a stretch receptor neuron of the stick insect (Carausius morosus)

Summary The ionic requirements for the action potentials recorded from the axon of the dorsal longitudinal stretch receptor inCarausius morosus have been studied using extracellular electrodes.In the intact preparation prolonged exposure to sodium-free, calcium-free, or magnesium-free salines produces no observable change in the amplitude of action potentials. Similarly, tetrodotoxin (1×10^–6 M) and cobaltous chloride (1×10^–2 M) are both ineffective in blocking the action potentials.In preparations in which the ionic barrier has been disrupted by removal of the nerve sheath the action potentials show sodium dependence. They are sustained in high sodium salines (150 mM) but are reversibly abolished in sodium-free salines. They are also reversibly abolished in 1×10^–6 M TTX, but unaffected by calcium-free or magnesium-free salines, or by cobaltous chloride (1×10^–2 M).It is concluded that the action currents in the axon of the stretch receptor are carried by sodium ions.