Nonselective cation channels promote persistent spiking in many neurons from a diversity of animals. In the hermaphroditic marinesnail, Aplysia californica, synaptic input to the neuroendocrine bag cell neurons triggers various cation channels, causing an ϳ30 min afterdischarge of action potentials and the secretion of egg-laying hormone. During the afterdischarge, protein kinase C is also activated, which in turn elevates hydrogen peroxide (H 2 O 2), likely by stimulating nicotinamide adenine dinucleotide phosphate oxidase. The present study investigated whether H 2 O 2 regulates cation channels to drive the afterdischarge. In single, cultured bag cell neurons, H 2 O 2 elicited a prolonged, concentration-and voltage-dependent inward current, associated with an increase in membrane conductance and a reversal potential of ϳϩ30 mV. Compared with normal saline, the presence of Ca 2ϩ-free, Na ϩ-free, or Na ϩ /Ca 2ϩ-free extracellular saline, lowered the current amplitude and left-shifted the reversal potential, consistent with a nonselective cationic conductance. Preventing H 2 O 2 reduction with the glutathione peroxidase inhibitor, mercaptosuccinate, enhanced the H 2 O 2-induced current, while boosting glutathione production with its precursor, N-acetylcysteine, or adding the reducing agent, dithiothreitol, lessened the response. Moreover, the current generated by the alkylating agent, N-ethylmaleimide, occluded the effect of H 2 O 2. The H 2 O 2-induced current was inhibited by tetrodotoxin as well as the cation channel blockers, 9-phenanthrol and clotrimazole. In current-clamp, H 2 O 2 stimulated burst firing, but this was attenuated or prevented altogether by the channel blockers. Finally, H 2 O 2 evoked an afterdischarge from whole bag cell neuron clusters recorded ex vivo by sharp-electrode. H 2 O 2 may regulate a cation channel to influence long-term changes in activity and ultimately reproduction.
