The long-term objectives of the proposed study are to elucidate the mechanism of action of environmentally important insecticides on the nerve membrane which is the most critical target site of various insecticides. The knowledge obtained through this research will have direct impact on our environmental concern, i.e., developments of effective therapeutic means for insecticide intoxication, and of newer insecticides which are more effective against insects yet safer for humans.
The specific aims are to clarify the nature of interactions of pyrethroid and DDT-type insecticides with nerve membrane ion channels which have been demonstrated to be mainly responsible for development of the symptoms of poisoning in animals. Advanced electrophysiological techniques developed in our laboratory over many years will be fully utilized, including intracellular and extracellular microelectrode, voltage clamp, patch clamp for whole cell and single channel recording, and intracellular perfusion. These techniques will be applied to cultured neuroblastoma cells, squid and crayfish giant axons, rat and crayfish neuromuscular junctions, and hippocampus slices from guinea-pigs. Six specific projects will be investigated: 1) Modification of kinetics of sodium channels by the insecticides will be analyzed in detail; 2) pyrethroids and DDT appear to bind to a membrane site near the gating machinery as approached through the lipid phase, and this hypothesis will be demonstrated by use of various chemical agents; 3) structure-activity relationship will be determined with special reference to stereospecificity; 4) the mechanism underlying the profound negative temperature coefficient of action of the insecticides will be elucidated at the channel level; 5) the mechanism underlying the drastic effects of the pyrethroids on calcium channels will be determined; and 6) controversial results concerning the effects of pyrethroids on neuroreceptors such as GABA receptor-channel complex will be re-examined and resolved. These studies are expected to provide the basis for the molecular mechanism of action of insecticides on the nervous system.
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