[Effect of synaptosomal cytosolic [3H]GABA pool depletion on secretory ability of alpha-latrotoxin].
alpha-Latrotoxin, a presynaptic neurotoxin from the venom of Latrodectus mactans tredecimguttatus, induces massive [3H]GABA release from rat brain synaptosomes as a result of interaction with either Ca(2+)-dependent (neurexin 1 alpha or Ca(2+)-independent (latrophilin) membrane receptor. The main aim of the study was to elucidate whether the binding of alpha-latrotoxin to different types of receptors led to [3H]GABA secretion from one pool or in each case the source of neurotransmitter differs: in the presence of Ca2+ exocytosis is induced, while in the absence of Ca(2+)--outflow by mobile membrane GABA transporter from cytoplasm. We examined the effect of the depletion of cytosolic [3H]GABA pool by competitive inhibitors of the GABA transporter (nipecotic acid and 2,4-diaminobutyric acid) on the alpha-latrotoxin-stimulated neurotransmitter release. We also compared the influence of these agents on neurosecretion, evoked by depolarization with that evoked by alpha-latrotoxin. Depolarization was stimulated by 4-aminopyridine in the Ca(2+)-containing saline and high KCl in Ca(2+)-free medium. In synaptosomes treated with nipecotic acid unstimulated [3H]GABA release was significantly augmented and high KCl-evoked Ca(2+)-independent [3H]GABA release was essentially inhibited. But under the same conditions neurosecretion stimulated by alpha-latrotoxin greatly raised with respect to the control response. The similar results were obtained with the synaptosomes treated with 2,4-diaminobutyric acid. Another way to determine which of GABA pool is the target of alpha-latrotoxin action lay in analysis of the toxin effects on the preliminary depolarized synaptosomes. alpha-Latrotoxin influence was diminished by the preceding depolarization by 4-aminopyridine in Ca2+ presence. But after the high KCl stimulation effect of alpha-latrotoxin didn't change. These data suggest that alpha-latrotoxin triggers neurotransmitter release from synaptic vesicles via exocytosis. We suppose that the type of membrane receptor does not determine the mechanism of GABA release evoked by the toxin.
Linets'ka
M V
MV
Palladin Institute of Biochemistry of NAS of Ukraine, Kyiv.
Storchak
L H
LH
Himmelreĭch
N H
NH
D015761:4-Aminopyridine / Q000494:pharmacology; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D003600:Cytosol / Q000378:metabolism; D009489:Neurosecretion / Q000187:drug effects; D009498:Neurotoxins / Q000494:pharmacology*; D009557:Nipecotic Acids / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013111:Spider Venoms / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism*; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000172:deficiency / Q000378:metabolism*
D000613:Aminobutyrates; D009498:Neurotoxins; D009557:Nipecotic Acids; D013111:Spider Venoms; D014316:Tritium; C030278:nipecotic acid; C005959:2,4-diaminobutyric acid; D005680:gamma-Aminobutyric Acid; C020763:alpha-latrotoxin; D015761:4-Aminopyridine