Interaction of tetramethrin and deltamethrin at the single sodium channel in rat hippocampal neurons

Type I and type II pyrethroids are known to modulate the sodium channel to cause persistent openings during depolarization and upon repolarization. Al though there are some similarities between the two types of pyrethroids in their actions on sodium channels, the pattern of modification of sodium cur rents is different between the two types of pyrethroids. In the present stu dy, interactions of the type I pyrethroid tetramethrin and the type II pyre throid deltamethrin at rat hippocampal neuron sodium channels were investig ated using the inside-out single-channel patch clamp technique. Deltamertri n-modified sodium channels opened much longer than tetramethrin-modified so dium channels. When 10 muM tetramethrin was applied to membrane patches tha t had been exposed to 10 muM deltamethrin, deltamertrin-modified prolonged single sodium currents disappeared and were replaced by shorter openings wh ich were characteristic of tetramethrin-modified channel openings. These si ngle-channel data are compatible with previous whole-cell competition study between type I and type II pyrethroids. These results are interpreted as b eing due to the displacement of the type II pyrethroid molecule by the type I pyrethroid molecule from the same binding site or to the allosteric inte raction of the two pyrethroid molecules as separate sodium channel sites. ( C) 2001 Elsevier Science Inc. All rights reserved.