title: The actions of presynaptic snake toxins on membrane currents of mouse motor nerve terminals.
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.
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives*; D000200:Action Potentials / Q000187:drug effects; D000077770:Amifampridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D007611:Aprotinin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D051379:Mice; D009045:Motor Endplate / Q000187:drug effects*; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000502:physiology*; D010741:Phospholipases A / Q000494:pharmacology; D054467:Phospholipases A2; D011188:Potassium / Q000502:physiology; D012910:Snake Venoms / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D000631:Aminopyridines; D007473:Ion Channels; D012910:Snake Venoms; D013757:Tetraethylammonium Compounds; D001030:Apamin; D019789:Tetraethylammonium; D007611:Aprotinin; D015761:4-Aminopyridine; D010741:Phospholipases A; D054467:Phospholipases A2; D000077770:Amifampridine; D011188:Potassium; D002118:Calcium