In conclusion our results show that

In conclusion, our results show that multiple receptor populations can be expressed when α4, β3 and δ mRNAs are injected into Xenopus oocytes and include β3 homomeric; α4β3; and β3δ receptors. The previously unidentified β3δ can be differentiated pharmacologically from either β3, α4β3 and α4β3δ receptors. We also show that a key feature of GABAARs that is likely to help explain differences in receptor pharmacology are the subunit interfaces within the receptor. For THIP and GABA, there is a wealth of evidence that these molecules bind at subunit interfaces located on the extracellular domain, interacting with the amino INF39 side chains of residues at the interface to determine their potency.
Experimental procedures
Acknowledgements We are very grateful to the Discipline of Pharmacology, The University of Sydney, for managing and maintaining the Xenopus laevis colony. HJL acknowledges support from the Australian Postgraduate Award Scheme. We acknowledge support from the National Health and Medical Research Council of Australia (NH&MRC Project Grant APP1003619 and APP1081733). Further funding support for PKA was provided by Imk Almene Fond, Denmark. The funding sources solely provided financial support and were not involved in any part of the conduct of the research.
GABAergic pesticides Our continuing ability to control pests that compete for food and fiber and transmit disease is dependent on the discovery of new compounds and biochemical targets that circumvent cross-resistance patterns and give a fresh start in pesticide management to maintain effective control [1]. Any novel target is therefore a valuable contribution not only to science but also to human welfare. The γ-aminobutyric acid (GABA) receptor (GABA-R) is the target for many insecticides, acaricides, anthelmintics and rodenticides of widely varied structures [2], [3], [4], [5], [6], [7], [8]. The extracellular and transmembrane domains also have multiple targets for other antagonists, agonists and modulators of various types. There are two recent insecticide chemotypes added to this list, i.e. the isoxazolines and meta-diamides which do not appear to have target site cross-resistance with any other type of insecticide and are therefore of special importance and the focus of this review (Fig. 1; Table 1).
GABA receptor
First generation non-competitive antagonists
Second generation non-competitive antagonists: NCA-II site
Allosteric modulator (AVE) The macrocyclic lactone ave (Fig. 4) was first used as an antiparasitic drug in 1981 and as an agricultural pesticide in 1985 [69] and several analogs and derivatives (such as emamectin benzoate, lepimectin and milbemectin) are also important commercial compounds [1]. Ivermectin was the essential agent in greatly reducing the incidence of river blindness in millions of people by controlling the schistisome vector [69]. Ave is a positive allosteric modulator of several ligand-gated channels including GABA- and glutamate-gated chloride channels and the α7-nicotinic receptor [70], [71], [72], [73]. The GABA-R target for ave is designated here as AVE. [3H]Ave is very effective as a radioligand for both insects and mammals in defining AVE action [55], [73]. [3H]Ave binding in Musca is not inhibited by GABA, fipronil or cyclodienes but is by flu. The C. elegans glutamate-gated chloride channel was important in structural definition of the RDL AVE site although a muscle glutamate receptor may be involved in contributing to or the cause of the toxicity [69], [70], [71], [72], [73], [74], [75]. Decreased binding is conferred by in silico mutations to A/Q6 and B1/S58 [75]. The ave binding site appears to be in an interstitial region between M2/M3 of one subunit and M1 of an adjacent subunit, a site which is proximal to the L9' to S16' pore region. Interactions modulate chloride flux at low ave concentrations and block the channel at high levels.
Four distinct binding sites