What does beta-bungarotoxin do at the neuromuscular junction?

Research output: Contribution to journalArticle

Abstract

beta-Bungarotoxin from the Taiwan banded krait, Bungarus multicinctus is a basic protein (pI=9.5), with a molecular weight of 21,800 consisting of two different polypeptide subunits. A phospholipase A(2) subunit named the A-chain and a non-phospholipase A(2) subunit named the B-chain, which is homologous to Kunitz protease inhibitors. The A-chain and the B-chain are covalently linked by one disulphide bridge. On mouse hemi-diaphragm nerve-muscle preparations, partially paralysed by lowering the external Ca(2+) concentration, beta-bungarotoxin classically produces triphasic changes in the contraction responses to indirect nerve stimulation. The initial transient inhibition of twitches (phase 1) is followed by a prolonged facilitatory phase (phase 2) and finally a blocking phase (phase 3). These changes in twitch tension are mimicked, to some extent, by similar changes to end plate potential amplitude and miniature end plate potential frequency. The first and second phases are phospholipase-independent and are thought to be due to the B-chain (a dendrotoxin mimetic) binding to or near to voltage-dependent potassium channels. The last phase (phase 3) is phospholipase dependent and is probably due to phospholipase A(2)-mediated destruction of membrane phospholipids in motor nerve terminals.
Original languageEnglish
Pages (from-to)107-118
Number of pages12
JournalToxicon
Volume39
Issue number1
DOIs
Publication statusPublished - 1 Jan 2001

Keywords

  • motor nerve terminals
  • bungaris-multicinctus venom
  • taiwan banded krait
  • amino-acid substitutions
  • phospholipase-a activity
  • p-bromophenacyl bromide
  • K+ channel
  • acetylcholine-release
  • potassium current
  • binding-sites

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