ABSTRACT
Arthropod venoms are sources of molecules that may be useful tools to investigate molecular mechanisms of putative new medicines and laboratory drugs. Here we show the effects of the compound agelaiatoxin-8 (AVTx8), isolated from Agelaia vicina venom, on γ-aminobutyric acid (GABA) neurotransmission in rat brain synaptosomes. Analysis reveals that AvTx8 is composed by 14 amino acid residues with a molecular weight (MW) of 1567 Da. AvTx8 increased GABA release and inhibited GABA uptake in synaptosomes from rat cerebral cortex. AvTx8 inhibited GABA uptake and increased GABA release in the presence of Ca+ , Na+ , and K+ channel blockers, suggesting that it acts directly on GABA transporters. In addition, AvTx8 significantly decreases GABA binding in synaptic membranes from rat brain cortex, suggesting that it also modulates the activity of GABA receptors. Moreover, AvTx8 decreased GAT-1- and GAT-3-mediated GABA uptake in transfected COS-7 cells. Accordingly, we suggest that AvTx8 modulates GABA neurotransmission and might provide a novel entry point for identifying a new class of GABA-modulating neuroprotective drugs.
Subject(s)
Synaptic Membranes/metabolism , Synaptic Transmission/drug effects , Synaptosomes/metabolism , Wasp Venoms , Wasps/chemistry , gamma-Aminobutyric Acid/metabolism , Animals , COS Cells , Chlorocebus aethiops , Ion Channels/antagonists & inhibitors , Ion Channels/metabolism , Rats , Rats, Wistar , Synaptic Membranes/pathology , Synaptosomes/pathology , Wasp Venoms/chemistry , Wasp Venoms/isolation & purification , Wasp Venoms/toxicityABSTRACT
Amphetamines elevate extracellular dopamine, but the underlying mechanisms remain uncertain. Here we show in rodents that acute pharmacological inhibition of the vesicular monoamine transporter (VMAT) blocks amphetamine-induced locomotion and self-administration without impacting cocaine-induced behaviours. To study VMAT's role in mediating amphetamine action in dopamine neurons, we have used novel genetic, pharmacological and optical approaches in Drosophila melanogaster. In an ex vivo whole-brain preparation, fluorescent reporters of vesicular cargo and of vesicular pH reveal that amphetamine redistributes vesicle contents and diminishes the vesicle pH-gradient responsible for dopamine uptake and retention. This amphetamine-induced deacidification requires VMAT function and results from net H(+) antiport by VMAT out of the vesicle lumen coupled to inward amphetamine transport. Amphetamine-induced vesicle deacidification also requires functional dopamine transporter (DAT) at the plasma membrane. Thus, we find that at pharmacologically relevant concentrations, amphetamines must be actively transported by DAT and VMAT in tandem to produce psychostimulant effects.
Subject(s)
Amphetamine/pharmacology , Brain/drug effects , Dopamine Agents/pharmacology , Dopamine Plasma Membrane Transport Proteins/drug effects , Dopamine/metabolism , Dopaminergic Neurons/drug effects , Locomotion/drug effects , Synaptic Vesicles/drug effects , Vesicular Monoamine Transport Proteins/antagonists & inhibitors , Animals , Animals, Genetically Modified , Brain/metabolism , Cocaine/pharmacology , Dopamine Plasma Membrane Transport Proteins/metabolism , Dopaminergic Neurons/metabolism , Drosophila melanogaster , HEK293 Cells , Humans , Image Processing, Computer-Assisted , Methamphetamine/pharmacology , Methylphenidate/pharmacology , Optical Imaging , Rats , Vesicular Monoamine Transport Proteins/drug effects , Vesicular Monoamine Transport Proteins/metabolismABSTRACT
We obtained a neurotoxic fraction (AcTx) from star fruit (Averrhoa carambola) and studied its effects on GABAergic and glutamatergic transmission systems. AcTx had no effect on GABA/glutamate uptake or release, or on glutamate binding. However, it specifically inhibited GABA binding in a concentration-dependent manner (IC(50)=0.89muM). Video-electroencephalogram recordings demonstrated that following cortical administration of AcTx, animals showed behavioral changes, including tonic-clonic seizures, evolving into status epilepticus, accompanied by cortical epileptiform activity. Chemical characterization of AcTx showed that this compound is a nonproteic molecule with a molecular weight less than 500, differing from oxalic acid. This neurotoxic fraction of star fruit may be considered a new tool for neurochemical and neuroethological research.
Subject(s)
Brain Chemistry/drug effects , Brain/drug effects , Convulsants/toxicity , Magnoliopsida/chemistry , Neurotoxins/toxicity , Plant Extracts/toxicity , Animals , Binding, Competitive , Brain/metabolism , Brain/physiopathology , Brain Chemistry/physiology , Convulsants/isolation & purification , Epilepsy/chemically induced , Epilepsy/metabolism , Epilepsy/physiopathology , Fruit/chemistry , Glutamic Acid/metabolism , Male , Mice , Molecular Weight , Neurons/drug effects , Neurons/metabolism , Neurotoxins/isolation & purification , Plant Extracts/chemistry , Plant Extracts/isolation & purification , Presynaptic Terminals/drug effects , Presynaptic Terminals/metabolism , Radioligand Assay , Rats , Rats, Wistar , Synaptic Transmission/drug effects , Synaptic Transmission/physiology , gamma-Aminobutyric Acid/metabolismABSTRACT
Venoms from several arthropods are recognized as useful sources of bioactive substances, such as peptides, acylpolyamines, and alkaloids, which show a wide range of pharmacological effects on synaptic transmission. In this work, we summarize and compile several biochemical and pharmacological aspects related to spider and wasp neurotoxins. Their inhibitory and stimulatory actions on ion channels, receptors, and transporters involved in mammalian and insect neurotransmission are considered.
Subject(s)
Neurotoxins/chemistry , Neurotoxins/pharmacology , Spider Venoms/chemistry , Wasp Venoms/chemistry , Animals , Brazil , Humans , Ion Channel Gating/drug effects , Sodium Channels/physiologyABSTRACT
It has previously been shown that the denatured crude extract of Agelaia vicina wasp venom inhibits glutamate and GABA uptake in rat cerebral cortex synaptosomes. To identify the components responsible for these effects, the neurotoxin AvTx 7 (molecular weight of 1210 Da) was isolated from A. vicina venom and its effects on glutamate neurotransmission investigated. AvTx 7 inhibits glutamate uptake in a dose-dependent and uncompetitive manner. AvTx 7 was found to stimulate the glutamate release in the presence of calcium and sodium channel blockers, suggesting that its action is not mediated through these channels. AvTx 7 potentiates glutamate release in the presence of K(+) channel blockers tetraethylammonium and 4-aminopyridine, indicating that the toxin may act through these drugs-sensible K(+) channels. We suggest that AvTx 7 can be a valuable tool to enhance our understanding of K(+) channels' involvement in the release of glutamate.
