Neuromuscular effects of some potassium channel blocking toxins from the venom of the scorpion Leiurus quinquestriatus hebreus

D L Marshall, H Vatanpour, A L Harvey, P Boyot, S Pinkasfeld, Y Doljansky, F Bouet, A Ménez

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Abstract

The scorpion venom Leiurus quinquestriatus hebreus was fractionated by chromatography in order to isolate toxins that affected binding of radiolabelled dendrotoxin to K+ channel proteins on synaptosomal membranes and that facilitated acetylcholine release in chick biventer cervicis nerve-muscle preparations. In addition to the previously characterized charybdotoxin, three toxins were isolated: 14-2, 15-1 and 18-2. Toxin 14-2 has a blocked N-terminus and because of low quantities, it has not been sequenced; 15-1 is a newly sequenced toxin of 36 residues with some overall homology to charybdotoxin and noxiustoxin; 18-2 is identical to charybdotoxin-2. The apparent Ki against dendrotoxin binding were: charybdotoxin, 3.8 nM; 14-2, 150 nM; 15-1, 50 nM; and 18-2, 0.25 nM. Toxin 14-2 (75 nM-1.5 microM) had a presynaptic facilitatory effect on neuromuscular preparations. Toxin 15-1 augmented responses to direct muscle stimulation, probably because it blocked Ca(2+)-activated K+ currents in muscle fibres. Toxin 18-2 (charybdotoxin-2) had a potent presynaptic facilitatory action, with less effect on direct muscle stimulation. This contrasts with the relatively weak neuromuscular effects of the highly homologous charybdotoxin. On a Ca(2+)-activated K+ current in mouse motor nerve endings, charybdotoxin and toxin 18-2 produced maximal block at around 100 nM, whereas 15-1 was inactive at 300 nM. Charybdotoxin can increase quantal content, but this is more likely to result from block of voltage-dependent K+ channels than Ca(2+)-activated channels: the increase in transmitter release occurred in conditions in which little IKCa would be present; higher concentration of charybdotoxin and longer exposure times were required to increase transmitter release than those needed to block IKCa, and the facilitatory effects of charybdotoxin and toxin 18-2 correlated more with their effects on dendrotoxin binding than on block of IKCa.
Original languageEnglish
Pages (from-to)1433-1443
Number of pages11
JournalToxicon
Volume32
Issue number11
DOIs
Publication statusPublished - Nov 1994

Keywords

  • acetylcholine
  • amino acid sequence
  • animals
  • competitive binding
  • charybdotoxin
  • chemical rractionation
  • chickens
  • high pressure liquid chromatography
  • ion exchange chromatography
  • drug dose-response relationship
  • elapid venoms
  • male
  • mice
  • molecular sequence data
  • neuromuscular junction
  • neurotoxins
  • phrenic nerve
  • potassium channel blockers
  • potassium channels
  • radioligand assay
  • scorpion venoms
  • amino acid sequence homology
  • structure-activity relationship
  • synaptosomes

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    Marshall, D. L., Vatanpour, H., Harvey, A. L., Boyot, P., Pinkasfeld, S., Doljansky, Y., Bouet, F., & Ménez, A. (1994). Neuromuscular effects of some potassium channel blocking toxins from the venom of the scorpion Leiurus quinquestriatus hebreus. Toxicon, 32(11), 1433-1443. https://doi.org/10.1016/0041-0101(94)90415-4