Abstract
The expression of a cloned Drosophila octopamine/tyramine receptor (OctyR99AB) is described in Xenopus oocytes. Agonist stimulation of OctyR99AB receptors increased intracellular Ca2+ levels monitored as changes in the endogenous inward Ca2+-dependent chloride current. The receptor is preferentially sensitive to biogenic amines with a single hydroxyl on the aromatic ring. The G-protein, Galphai, appears to be involved in the coupling of the receptor to the production of intracellular calcium signals, since the effect is pertussis-toxin sensitive and is blocked or substantially reduced in antisense knockout experiments using oligonucleotides directed against Galphai but not by those directed against Galphao, Galphaq and Galpha11. The increase in intracellular calcium levels induced by activation of the OctyR99AB receptor can potentiate the ability of activation of a co-expressed beta2-adrenergic receptor to increase oocyte cyclic AMP levels. A comparison of the pharmacological coupling of OctyR99AB to different second messenger systems when expressed in Xenopus oocytes with previous studies on the expression of the receptor in a Chinese hamster ovary cell line suggests that the property of agonist-specific coupling of the receptor to different second messenger systems may be cell-specific, depending upon the G-protein environment of any particular cell type.
