Differential blocking actions of 4'-ethynyl-4-n-propylbicycloorthobenzoate (EBOB) and gamma-hexachlorocyclohexane (gamma-HCH) on gamma-aminobutyric acid- and glutamate-induced responses of American cockroach neurons.

Abstract

4'-Ethynyl-4-n-propylbicycloorthobenzoate (EBOB) has been employed extensively as a radioligand in binding assays to evaluate the pharmacology of gamma-aminobutyric acid (GABA)-gated Cl- channels (GABARs) of insects and mammals, and gamma-hexachlorocyclohexane (gamma-HCH) was used as an insecticide targeting insect GABARs. Since recent studies have shown that not only GABARs but also glutamate-gated chloride channels (GluCls) are blocked by picrotoxinin, dieldrin and fipronil, the actions of EBOB and gamma-HCH on native GABARs and GluCls of terminal abdominal ganglion neurons in American cockroach (Periplaneta americana) were tested using patch-clamp electrophysiology. A marked run-down of the GABA- and glutamate-induced responses of the cockroach neurons occurred, when a standard pipette solution was employed, but addition of pyruvate to the solution permitted stable recordings of these responses. With this solution, EBOB and gamma-HCH were found to block not only the GABA- but also glutamate-gated responses, with the actions augmented by repeated co-application with the agonists. It was also found that prolonged pre-application of EBOB and gamma-HCH prior to co-application with GABA and glutamate resulted in enhanced blocking actions, indicating resting-state actions of the blockers. The blocking actions of EBOB and gamma-HCH on the GABA- and glutamate-induced responses were compared by determining IC50 values under steady state condition. The IC50 values for the actions of EBOB on GABAR and GluCls differed less than those of gamma-HCH.

• Authors: Makoto Ihara, Chiharu Ishida, Hiroshi Okuda, Yoshihisa Ozoe, Kazuhiko Matsuda
• Journal: Invertebrate neuroscience : IN (Invert Neurosci) Vol. 5 Issue 3-4 Pg. 157-64 (Nov 2005) ISSN: 1354-2516 [Print] Germany
• PMID: 16195902 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Bridged Bicyclo Compounds, Heterocyclic
• Chloride Channels
• Insecticides
• Receptors, GABA
• Receptors, Glutamate
• 1-(4-ethynylphenyl)-4-propyl-2,6,7-trioxabicyclo(2.2.2)octane
• Glutamic Acid
• gamma-Aminobutyric Acid
• Hexachlorocyclohexane

Topics

• Animals
• Bridged Bicyclo Compounds, Heterocyclic (pharmacology)
• Chloride Channels (drug effects)
• Dose-Response Relationship, Drug
• Glutamic Acid (metabolism)
• Hexachlorocyclohexane (pharmacology)
• Insecticides (pharmacology)
• Neurons (drug effects)
• Patch-Clamp Techniques
• Periplaneta
• Receptors, GABA (drug effects)
• Receptors, Glutamate (drug effects)
• gamma-Aminobutyric Acid (metabolism)