[Nitrites block the Ca-dependent habituation of neurons at the level of an electroexcitable membrane: a possible role for nitric oxide].

Penetration of Ca2+ into neuron have been shown earlier to be mainly responsible for the cell habituation to repeated intracellular stimulation by impulse depolarizing current. Considering the key role of nitric oxide (NO) in regulation of intracellular Ca2+ turnover, effects of exogenous nitrite NaNO2, used as a source of NO, on plasticity properties of the electrostimulated membrane were studied in the identified habituating and non-habituating neurones of snail (Gastropoda) brain. The sodium nitrite 10(-6)-10(-4) M was found to inhibit, with a latent period 10-30 min, the ability of the habituating neurones to get accustomed to stimulation; this phenomenon was oscillatory. The concentration of nitrite 10(-3) M affected irreversibly the habituation. Serotonin potentiated the inhibitory effect of nitrite on habituation and vice versa nitrite augmented the serotonin effect on habituation of the same neurones. The exogenous nitrite sensitized the non-habituating neurones to intracellular stimulation. These data suggest that nitrite affects the plasticity properties of the electrostimulated neurone membrane. Besides, these results and well-known properties of NO allowed one to assume that NO-dependent regulation of intracellular Ca2+ was responsible for the phenomenon observed as well as that NO- and serotoninergic systems appear to interact in the snail brain.