Apparent block of K+ currents in mouse motor nerve terminals by tetrodotoxin, mu-conotoxin and reduced external sodium.
1. In mouse triangularis sterni nerve-muscle preparations, reduced extracellular Na+ concentrations and low concentrations of the Na+ channel blocking toxins tetrodotoxin (TTX, 18-36 nM) and mu-conotoxin GIIIB (0.4-2.0 microM) selectively decreased the amplitude of the component of perineural waveforms associated with nerve terminal K+ currents, without affecting the main Na+ spike. 2. Intracellular recording of endplate potentials (e.p.ps) and miniature endplate potentials (m.e.p.ps) from triangularis sterni preparations revealed that TTX and mu-conotoxin GIIIB depressed the evoked quantal release of acetylcholine without significant effects on m.e.p.p. amplitude, frequency or time constant of decay. 3. The apparent block of K+ current by low concentrations of TTX and mu-conotoxin is probably not a direct effect on K+ channels but results from a decrease in the passive depolarization of nerve terminals following blockade of a small proportion of axonal Na+ channels.
Braga
M F
MF
Department of Physiology and Pharmacology, University of Strathclyde, Glasgow.
Anderson
A J
AJ
Harvey
A L
AL
Rowan
E G
EG
D000818:Animals; D020916:Conotoxins; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology*
D020916:Conotoxins; D010456:Peptides, Cyclic; D015221:Potassium Channels; D015222:Sodium Channels; C046101:conotoxin GIII; D013779:Tetrodotoxin; D012964:Sodium; D011188:Potassium