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Sci Rep
2014 Aug 26;4:6190. doi: 10.1038/srep06190.
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GluCl a target of indole alkaloid okaramines: a 25 year enigma solved.
Furutani S
,
Nakatani Y
,
Miura Y
,
Ihara M
,
Kai K
,
Hayashi H
,
Matsuda K
.
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In 1989, indole alkaloid okaramines isolated from the fermentation products of Penicillium simplicissimum were shown to be insecticidal, yet the mechanism of their toxicity to insects remains unknown. We therefore examined the action of okaramine B on silkworm larval neurons using patch-clamp electrophysiology. Okaramine B induced inward currents which reversed close to the chloride equilibrium potential and were blocked by fipronil. Thus it was tested on the silkworm RDL (resistant-to-dieldrin) γ-aminobutyric-acid-gated chloride channel (GABACl) and a silkworm L-glutamate-gated chloride channel (GluCl) expressed in Xenopus laevis oocytes. Okaramine B activated GluCl, but not RDL. GluCl activation by okaramines correlated with their insecticidal activity, offering a solution to a long-standing enigma concerning their insecticidal actions. Also, unlike ivermectin, okaramine B was inactive at 10 μM on human α1β2γ2 GABACl and α1β glycine-gated chloride channels and provides a new lead for the development of safe insect control chemicals.
Figure 1. Structures of okaramines A, B, 4′,5′-dihydrookaramine B (okaramine B-H2), I and Q.
Figure 2. Action of okaramine B on the membrane currents of silkworm larval neurons as measured with whole-cell patch-clamp electrophysiology (a–d) and on silkworm larval RDL γ-aminobutyric-acid-gated chloride channel (GABACl) (e, f) and L-glutamate-gated chloride channel (GluCl) (g) expressed in Xenopus laevis oocytes as measured with two-electrode voltage-clamp electrophysiology.Okaramine B was applied via U-tube, whereas antagonists were bath-applied to the neurons. (a) Inward current induced by okaramine B at 1 μM and the effect of nicotinic receptor antagonist mecamylamine (1 μM) applied for 1 min prior to co-application with 1 μM okaramine B. (b) Inward current induced by okaramine B at 1 μM and the effect of ligand-gated chloride channel blocker fipronil (10 μM) applied for 1 min prior to co-application with 1 μM okaramine B. (c) Inward current induced by 1 μM okaramine B at various holding potentials. (d) Current-voltage relationship at two different extracellular chloride concentrations. Each plot indicates the mean ± standard error of repeated experiments (n = 3). (e) Five min after recording the response to 30 μM GABA of RDL, 10 μM okaramine was bath-applied. (f) Okaramine B was bath-applied at 10 μM for 1 min prior to co-application with 30 μM GABA. Okaramine B had a minimal impact on the GABA response RDL. (g) Five min after recording the response to 100 μM L-glutamate of GluCl, 1 and 3 μM okaramine B was bath-applied with at 5-min interval.
Figure 3. Concentration-response relationships of okaramines A, B, 4′,5′-dihydrookaramine B (okaramine B-H2), I and Q for the Cl− current inducing activity on the silkworm neurons and the GluCl activating activity, and correlations of these two activities with the insecticidal activity on the silkworm larvae.(a) Concentration-response relationship for the chloride-current inducing activity on the silkworm larval neuron. (b) Concentration-response relationship for the GluCl activating activity. Each plot indicates the mean ± standard error of the mean of repeated experiments (n = 4). (c) 3D plot for the relationship of the GluCl activating activity (X axis), and the Cl− current inducing activity on the larval neuron (Y axis) with the insecticidal activity (n = 3) (Z axis). Each sphere plot in (c) is projected to X-Y, X-Z and Y-Z planes to show its position in each plane.
Figure 4. Actions of okaramine B on human α1β2γ2 GABACl and α1β glycine-gated chloride channel (GlyCl) expressed in Xenopus laevis oocytes.(a) Three minutes after recording a response to 30 μM GABA, 10 μM okaramine B was bath-applied to oocytes expressing the human α1β2γ2 GABACl. After 3 min wash, 10 μM ivermectin was bath-applied. (b) Okaramine B (10 μM) was pre-applied for 1 min prior to co-application with 30 μM GABA to the α1β2γ2 GABACl. (c) Three minutes after recording a response to 100 μM glycine, 10 μM okaramine B was bath-applied to oocytes expressing the human α1β GlyCl. After 3 min wash, 10 μM ivermectin was bath-applied. (d) Okaramine B (10 μM) was pre-applied for 1 min prior to co-application with 100 μM glycine to oocytes expressing the α1β GlyCl. All the results were reproducible (n = 4).
Ascher,
Studies on the mechanism of action of acetylcholine antagonists on rat parasympathetic ganglion cells.
1979, Pubmed
Ascher,
Studies on the mechanism of action of acetylcholine antagonists on rat parasympathetic ganglion cells.
1979,
Pubmed
Baran,
Short, enantioselective total synthesis of okaramine N.
2003,
Pubmed
Buckingham,
Insect GABA receptors: splicing, editing, and targeting by antiparasitics and insecticides.
2005,
Pubmed
Gengs,
The target of Drosophila photoreceptor synaptic transmission is a histamine-gated chloride channel encoded by ort (hclA).
2002,
Pubmed
,
Xenbase
Gisselmann,
Two cDNAs coding for histamine-gated ion channels in D. melanogaster.
2002,
Pubmed
,
Xenbase
Hardie,
A histamine-activated chloride channel involved in neurotransmission at a photoreceptor synapse.
1989,
Pubmed
Hayashi,
Okaramines H and I, new okaramine congeners, from aspergillus aculeatus.
1999,
Pubmed
Hayashi,
Okaramine G, a New Okaramine Congener from Penicillium simplicissimum ATCC 90288.
1998,
Pubmed
Hewitt,
A concise total synthesis of (+)-okaramine C.
2004,
Pubmed
Hirata,
A fungal metabolite asperparaline a strongly and selectively blocks insect nicotinic acetylcholine receptors: the first report on the mode of action.
2011,
Pubmed
,
Xenbase
Ihara,
Diverse actions of neonicotinoids on chicken alpha7, alpha4beta2 and Drosophila-chicken SADbeta2 and ALSbeta2 hybrid nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes.
2003,
Pubmed
,
Xenbase
Ikeda,
Fipronil modulation of glutamate-induced chloride currents in cockroach thoracic ganglion neurons.
2003,
Pubmed
Ikeda,
Fipronil modulation of gamma-aminobutyric acid(A) receptors in rat dorsal root ganglion neurons.
2001,
Pubmed
Raymond,
Novel animal-health drug targets from ligand-gated chloride channels.
2002,
Pubmed
Roe,
Total Synthesis of (+)-okaramine J featuring an exceptionally facile N-reverse-prenyl to C-prenyl aza-Claisen rearrangement.
2003,
Pubmed
Schnizler,
A novel chloride channel in Drosophila melanogaster is inhibited by protons.
2005,
Pubmed
,
Xenbase
Shimomura,
Role in the selectivity of neonicotinoids of insect-specific basic residues in loop D of the nicotinic acetylcholine receptor agonist binding site.
2006,
Pubmed
,
Xenbase
Shiono,
Okaramines N, O, P, Q and R, new okaramine congeners, from Penicillium simplicissimum ATCC 90288.
2000,
Pubmed
Shiono,
Effect of the azetidine and azocine rings of okaramine B on insecticidal activity.
2000,
Pubmed
Wolstenholme,
Glutamate-gated chloride channels.
2012,
Pubmed
Zheng,
Identification of two novel Drosophila melanogaster histamine-gated chloride channel subunits expressed in the eye.
2002,
Pubmed
