High-affinity [3H]octopamine-binding sites in Drosophila melanogaster: Interaction with ligands and relationship to octopamine receptors

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Abstract

  • 1.

    1. [3H]Octopamine binds to a particulate preparation from heads of Drosophila melanogaster at a level of 0.5 ± 0.1 pmol/mg protein, with an apparent dissociation constant of 6.0 ± 0.9 × 10−9M at 26°C. The binding is reduced or abolished by heat, trypsin, detergents, sulfhydryl reagents and EDTA.

  • 2.

    2. Low concentrations of MgCl2 or CaCl2 increase binding but high ionic strength is inhibitory.

  • 3.

    3. Low concentrations of dihydroergotamine, phentolamine, clonidine, chlorimipramine and chlorpromazine, but not of serotonin and propranolol, displace the labeled biogenic amine from its binding sites.

  • 4.

    4. The stable GTP analogue, guanosine-5′-(β-γ-imido)triphosphate (Gpp(NH)p), at the μM range, decreases the maximal number of the high-affinity [3H]octopamine-binding sites.

  • 5.

    5. The properties of the [3H]octopamine-binding sites are compared to the properties of octopamine receptors as revealed by stimulation of adenylate cyclase in insects, including Drosophila.

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