The actions of presynaptic snake toxins on membrane currents of mouse motor nerve terminals

J Physiol. 1987 May;386:455-63. doi: 10.1113/jphysiol.1987.sp016544.

Abstract

1. The m. triangularis sterni of the mouse was used to investigate the actions of dendrotoxin, beta-bungarotoxin, crotoxin, taipoxin, bee venom phospholipase A2, aprotinin and apamin on presynaptic currents which flow inside the perineural sheath of nerve bundles upon nerve stimulation. 2. Neither the fast K+ current (IK,f) nor the Ca2+-dependent K+ current IK(Ca) (unmasked after blockade of IK,f by 3,4-diaminopyridine) was affected by the neurotoxins and drugs mentioned. 3. Inhibition of both IK,f and IK(Ca) by tetraethylammonium (30 mM) prolonged presynaptic depolarization owing to Ca2+ influx through fast and slow Ca2+ channels. Additional application of dendrotoxin, beta-bungarotoxin, crotoxin or taipoxin in the nanomolar range caused further prolongation of Ca2+ influx, presumably due to blockade of slowly activating K+ current (IK,s). Onset of toxin effects was immediate and could not be reversed by washing for 60 min. 4. Similar prolongation of slow Ca2+ current was effected by 3,4-diaminopyridine, whereas addition of apamin, aprotinin or phospholipase A2 left the signals unchanged. 5. These data indicate that facilitatory actions of dendrotoxin, beta-bungarotoxin, taipoxin and crotoxin are mediated by an increase of Ca2+ entry into nerve terminals. The actions of these toxins are discussed in terms of a blockade of presynaptic K+ channels with slow activation kinetics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Aminopyridine* / analogs & derivatives*
  • Action Potentials / drug effects
  • Amifampridine
  • Aminopyridines / pharmacology
  • Animals
  • Apamin / pharmacology
  • Aprotinin / pharmacology
  • Calcium / physiology
  • In Vitro Techniques
  • Ion Channels / drug effects
  • Mice
  • Motor Endplate / drug effects*
  • Neuromuscular Junction / drug effects*
  • Neuromuscular Junction / physiology*
  • Phospholipases A / pharmacology
  • Phospholipases A2
  • Potassium / physiology
  • Snake Venoms / pharmacology*
  • Tetraethylammonium
  • Tetraethylammonium Compounds / pharmacology

Substances

  • Aminopyridines
  • Ion Channels
  • Snake Venoms
  • Tetraethylammonium Compounds
  • Apamin
  • Tetraethylammonium
  • Aprotinin
  • 4-Aminopyridine
  • Phospholipases A
  • Phospholipases A2
  • Amifampridine
  • Potassium
  • Calcium