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Differential Actions of Fipronil and Dieldrin Insecticides on GABA-Gated Chloride Channels in Cockroach Neurons
Fipronil and dieldrin are known to inhibit GABA receptors in both mammals and insects. However, the mechanism of selective toxicity of these insecticides between mammals and insects remains to be seen. One possible mechanism is that insect GABA receptors are more sensitive than mammalian GABA A rece...
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Published in: | The Journal of pharmacology and experimental therapeutics 2003-09, Vol.306 (3), p.914-924 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Fipronil and dieldrin are known to inhibit GABA receptors in both mammals
and insects. However, the mechanism of selective toxicity of these
insecticides between mammals and insects remains to be seen. One possible
mechanism is that insect GABA receptors are more sensitive than mammalian
GABA A receptors to fipronil and dieldrin. We examined differential
actions of fipronil and dieldrin on GABA-gated chloride channels in insects
and compared them with the data on mammalian GABA A receptors.
Neurons were acutely dissociated from the American cockroach thoracic ganglia,
and currents evoked by GABA were recorded by the whole-cell patch-clamp
technique. GABA-evoked currents were carried by chloride ions, blocked by
picrotoxinin, but not by bicuculline. Fipronil inhibited GABA currents with an
IC 50 value of 28 nM, whereas dieldrin exhibited a dual action
potentiation with an EC 50 value of 4 nM followed by inhibition with
an IC 50 value of 16 nM. Fipronil and dieldrin acted on the resting
receptor at comparable rates, whereas fipronil blocked the activated receptor
10 times faster than dieldrin. Fipronil inhibition was partially reversible,
whereas dieldrin inhibition was irreversible. Fipronil was 59 times more
potent on cockroach GABA receptors than on rat GABA A receptors.
However, the potentiating and inhibitory potencies of dieldrin in cockroach
GABA receptors were comparable with those in rat GABA A receptors.
It was concluded that the higher toxicity of fipronil in insects than in
mammals is due partially to the higher sensitivity of GABA receptors. The
mechanism of dieldrin's selective toxicity must lie in factors other than the
sensitivity of GABA receptors. |
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ISSN: | 0022-3565 1521-0103 |
DOI: | 10.1124/jpet.103.051839 |