γ-Aminobutyric Acid Receptor Complex of Insect CNS: Characterization of a Benzodiazepine Binding Site |
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Authors: | Timothy Robinson David MacAllan George Lunt Martin Battersby |
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Institution: | Department of Biochemistry, The University of Bath, Bath;England;ICI Plant Protection Division, Jealott's Hill Research Station, Bracknell, Berkshire, England |
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Abstract: | The specific binding of N-methyl-3H]flunitrazepam (3H]FNZP) to a membrane fraction from the supraoesophageal ganglion of the locust (Schistocerca gregaria) has been measured. The ligand binds reversibly with a KD of 47 nM. The binding is Ca2+-dependent, a property not found for the equivalent binding site in vertebrate brain. The pharmacological characteristics of the locust binding site show similarities to both central and peripheral benzodiazepine receptors in mammals. Thus binding is enhanced by gamma-aminobutyric acid (GABA), a feature of mammalian central receptors, whereas the ligand Ro 5-4864 was more effective in displacing 3H]FNZP than was clonazepam, which is the pattern seen in mammalian peripheral receptors. The locust benzodiazepine binding site was photoaffinity-labelled by 3H]FNZP, and two major proteins of Mr 45K and 59K were specifically labelled. In parallel experiments with rat brain membranes a single major protein of Mr 49K was labelled, a finding in keeping with many reports in the literature. We suggest that the FNZP binding site described here is part of the GABA receptor complex of locust ganglia. The insect receptor appears to have the same general organization as its mammalian counterpart but differs significantly in its detailed properties. |
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Keywords: | γ-Aminobutyric acid receptor complex [N-methyl-3H] Flunitrazepam Locust (Schistocerca gregaria) Ganglion Benzodiazepine binding site |
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