The effect of hydrogen peroxide and copper on the membrane potential of Retzius nerve cell. Extracellular application of 1 mM H₂O₂ and 0.02 mM Cu(II) depolarized the cell membrane potential of −53 mV by 9 mV.

The characteristic changes in the action potential of Retzius nerve cells produced by 1 mM H₂O₂ and 0.02 mM Cu(II). (A) In the control leech Ringer, the Retzius cell have action potential of 48 mV with a duration of 7.4 ms. The amplitude of action potentials decreased, while duration increased in a progressive way along the drug exposure time. (B) Repetitive firing recorded in Retzius nerve cell 10 and 15 min after the application of H₂O₂/Cu(II).

The inhibition of the outward K⁺ current by H₂O₂/Cu(II). Original tracings of the outward K⁺ current of Retzius nerve cell evoked by a 300 ms depolarizing pulse in the Tris Ringer (A) and presence of 1 mM H₂O₂ and 0.02 mM Cu(II) (B) for 10 min. At a clamp voltage of +25 mV, the fast and slow steady part of the K⁺ outward currents were reduced by 70% after exposure of the Retzius neurons to H₂O₂/Cu(II).

The effects of H₂O₂/Cu(II) on the outward K⁺ current of Retzius nerve cells. The current-voltage relationship at the peak of the K⁺ outward current (Ikr) and at the end of stimulation (Iks) in the absence (open symbols) and presence (solid symbols) of H₂O₂ (1 mM) and 0.02 mM Cu(II). Ikr, rapid outward K⁺ current; Iks, slow outward K⁺ current.

The effects of the antioxidants on the duration of Retzius nerve cells' action potentials prolonged by H₂O₂/Cu(II). The neurotoxic effect of H₂O₂/Cu(II) on spontaneous spike electrogenesis of the Retzius neurons was reduced in the presence of the dimethylthiourea (1 mM) and dimethyl sulfoxide (1%), but not the mannitol (5 mM). The measures are expressed as mean±s.d.; *P<0.05 compared with control condition.