The Original Study Of β-Agkistrodotoxin Effect On Ca～(2+)-dependent Glutamate, Aspartate, Glycine And GABA Release From Rat Brain Synaptosomes

β-Agkistrodotoxin(β-AgTX) is a presynaptic neurotoxin. With the methods of enzyme-linked fluorescence measurement and amino acid assay the experiments examined the action of β-Agkistrodotoxin on KCl depolarization evoked glutamate (Glu), aspartate (Asp), glycine (Gly) and ?-aminobutyric acid (GABA) release from the isolated cerecortical synaptosomes, and its effect on the depolarization of synaptic membranes was also investigated. All results are as follows:1. Incubated with synaptosomes at 370C for 30 min, β-AgTX effectively inhibits 50mM KCl induced Ca2+-dependent Glu transmitter release. The inhibition of β-AgTX is concentration-dependent, with 18nM attaining a maximal inhibition of 80±2% of Ca2+ control. 2. 18nMβ-AgTX has no significant effect on calcium ionophore ionomycin stimulated Ca2+-dependent Glu transmitter release. It is suggested that the inhibition result from the reduction of Ca2+ influx but not the action on release machinery itself. 3. Amino acid assay found that besides the release of Glu, preincubation with synaptosomes at 370C for 30 min enabled β-AgTX to reduce KCl induced Asp, Gly, GABA release from synaptosomes by 90±3%, 94.5±2% and 95±1.5%, however ionomycin evoked release of these transmitters is not significantly affected. It is indicatedβ-AgTX has a common inhibitory effect on the release of these transmitters by a resemble mechanism. 1. 4. Incubated with DISC2(5) labeled synaptosomes at 370C for 30 minβ-AgTX blocked 53±4% of KCl induced membrane depolarization. In sum β-AgTX inhibits Ca2+-dependent Glu, Asp, Gly and GABA transmitter release through reducing Ca2+ influx directly or indirectly, implying the acting site of β-AgTX on presynaptic fragments is likely to be a common functional component involved in transmitter exocytosis upstream of activation of voltage-dependent Ca2+ channels.