The neurotoxicity of environmental pollutants: the effects of tin (Sn2+) on acetylcholine-induced currents in greater pond snail neurons.

Inorganic and organic tin compounds present in aqueous ecosystems have diverse effects on the behavior of living organisms. With the aim of identifying possible correlates of these actions, we studied the effects of both types of Sn2+. The effects of SnCl2 and Sn(CH3)2 on acetylcholine-activate currents were studied on identified neurons of the mollusk Lymnaea stagnalis L. using a two-microelectrode membrane potential clamping technique and by intracellular dialysis with potential and ion concentration clamping. Experiments were performed on single neurons after isolation and on whole ganglion preparations. SnCl2 decreased acetylcholine-induced influx currents; the effect was dose-dependent. The effective threshold concentration, measured by the two-microelectrode membrane potential clamping method, was 0.1 microM, with saturation occurring at 5 microM SnCl2. After a 10-min preapplication of SnCl2, the effect was stronger (20%) than after treatment for 3 min (7%). Similar results were obtained after application of tin using the intracellular dialysis method with potential and ion concentration clamping. After preapplication of 10 microM SnCl2 for 1 min, acetylcholine-induced influx currents decreased by 41%, we compared differences in the effects induced by inorganic and organic tin compounds. Sn(CH3) induced a decrease in the amplitude of acetylcholine-induced currents in the same way as inorganic tin. The effect of Sn(CH3)2 was irreversible and stronger as the preapplication time increased. These results support the previous conclusion that agonist-activated channels are an important target for the actions of toxic metals. It is concluded that direct actions on neuron membranes represent an important component in the modulation of synaptic transmission and that this should be considered in studies of the mechanisms of toxicity of tin.