Mechanism of beta-bungarotoxin in facilitating spontaneous transmitter release at neuromuscular synapse.
The mechanism of the action of beta-bungarotoxin (beta-BuTx) in the facilitation of spontaneous transmitter release at neuromuscular synapse was investigated in Xenopus cell culture using whole-cell patch clamp recording. Exposure of the culture to beta-BuTx dose-dependently enhances the frequency of spontaneous synaptic currents (SSCs). Buffering the rise of intracellular Ca2+ with BAPTA-AM hampered the facilitation of SSC frequency induced by beta-BuTx. The beta-BuTx-enhanced SSC frequency was reduced when the pharmacological Ca2+ -ATPase inhibitor thapsigargin was used to deplete intracellular Ca2+ store. Application of membrane-permeable inhibitors of inositol 1,4,5-trisphosphate (IP3) but not ryanodine receptors effectively occluded the increase of SSC frequency elicited by beta-BuTx. Treating cells with either wortmannin or LY294002, two structurally different inhibitors of phosphatidylinositol 3-kinase (PI3K) and with phospholipase C (PLC) inhibitor U73122, abolished the beta-BuTx-induced facilitation of synaptic transmission. The beta-BuTx-induced synaptic facilitation was completely abolished while there was presynaptic loading of the motoneuron with GDPbetaS, a non-hydrolyzable GDP analogue and inhibitor of G protein. Taken collectively, these results suggest that beta-BuTx elicits Ca2+ release from the IP3 sensitive intracellular Ca2+ stores of the presynaptic nerve terminal. This is done via PI3K/PLC signaling cascades and G protein activation, leading to an enhancement of spontaneous transmitter release.
Liou
Jau-Cheng
JC
Department of Biological Sciences, National Sun Yat-sen University, No 70, Lein-Hai Rd., Kaohsiung 804, Taiwan. netliou@mail.nsysu.edu.tw
Kang
Kai-Hsiang
KH
Chang
Long-Sen
LS
Ho
Shih-Yin
SY
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000831:Animals, Newborn; D001896:Boron Compounds / Q000494:pharmacology; D002038:Bungarotoxins / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005233:Fatty Alcohols / Q000494:pharmacology; D066298:In Vitro Techniques; D009469:Neuromuscular Junction / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010741:Phospholipases A / Q000494:pharmacology; D014982:Xenopus laevis
D001896:Boron Compounds; D002038:Bungarotoxins; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005233:Fatty Alcohols; D018377:Neurotransmitter Agents; C476391:xestoaminol C; D004533:Egtazic Acid; C109986:2-aminoethoxydiphenyl borate; D010741:Phospholipases A; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium