The role of Ins(1,4,5)P(3) in signal transduction of the metabolic neuropeptide Mem-CC in the cetoniid beetle,Pachnoda sinuata |
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Authors: | Auerswald Lutz Gäde Gerd |
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Institution: | Zoology Department, University of Cape Town, Rondebosch 7701, South Africa |
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Abstract: | We have investigated the role of inositol triphosphate, Ins(1,4,5)P3, in the transduction of the hypertrehalosaemic and hyperprolinaemic signal of the endogenous neuropeptide Mem-CC in the cetoniid beetle Pachnoda sinuata. Flight and injection of Mem-CC into the haemocoel of the beetle induce an increase of Ins(1,4,5)P3 levels in the fat body of the beetle. When Mem-CC is co-injected with U 73122, which is an inhibitor of phospholipase C, this effect is abolished. Mem-CC also elevates Ins(1,4,5)P3 concentration in fat body pieces in vitro. The increase in Ins(1,4,5)P3 levels is tissue-specific and does not occur in brain and flight muscles. Elevation of the Ins(1,4,5)P3 levels upon injection of Mem-CC is time- and dose-dependent: the maximum response is reached after 3 min and a dose of 10 pmol is needed. Compounds that mimic the action of cAMP (cpt-cAMP, forskolin) do not influence the concentration of Ins(1,4,5)P3, while those that stimulate G-proteins (aluminium fluoride and cholera toxin) cause an increase of Ins(1,4,5)P3 levels. The application (in vivo and in vitro) of F-Ins(1,4,5)P3, an Ins(1,4,5)P3 analogue that penetrates the cell membrane, causes a mobilisation of carbohydrate reserves via the activation of glycogen phosphorylase but does not stimulate proline synthesis. In addition, U 73122 abolishes the hypertrehalosaemic but not the hyperprolinaemic effect of Mem-CC. The results suggest that the hypertrehalosaemic signal of Mem-CC is mediated via an increase of Ins(1,4,5)P3 levels in the fat body of P. sinuata. |
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Keywords: | Ins(1 4 5)P3 Second messenger Proline Carbohydrates Insect flight AKH peptides Fruit beetle Pachnoda sinuata |
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