Background: Tyramine (TA) and octopamine (OA) are considered to be the invertebrate counterparts of the vertebrate adrenergic transmitters. Because these two phenolamines are the only biogenic amines whose physiological significance is presumably restricted to invertebrates, the attention of pharmacologists has been focused on the corresponding receptors, which are believed to represent promising targets for novel insecticides. For example, the formamidine pesticides, such as chlordimeform and amitraz, have been shown to activate OA receptors.
Results: A full-length cDNA (designated CsTyR1) from the rice stem borer, Chilo suppressalis (Walker), has been obtained through homology cloning in combination with rapid amplification of cDNA ends/polymerase chain reaction (RACE-PCR). The mRNA of CsTyR1 is present in various tissues, including hemocytes, fat body, midgut, Malpighian tubules, nerve cord and epidermis, and it is found predominantly in the larval nerve cord with 16-80-fold enrichment compared with other tissues. The authors generated a HEK 293 cell line stably expressing CsTyR1 in order to examine functional and pharmacological properties of this receptor. Both TA and OA at 0.01-100 µM can reduce forskolin-stimulated intracellular cAMP levels in a dose-dependent manner (TA, EC(50) = 369 nM; OA, EC(50) = 978 nM). In agonist assays, activation of CsTyR1 by clonidine and amitraz but not by naphazoline and chlordimeform can also significantly inhibit forskolin-stimulated cAMP production. The inhibitory effect of TA at 10 µM is eliminated by coincubation with yohimbine, phentolamine or chlorpromazine (each 10 µM).
Conclusion: This study represents a comprehensive molecular and pharmacological characterisation of a tyramine receptor in the rice stem borer.
Copyright © 2012 Society of Chemical Industry.