Apparent block of K+ currents in mouse motor nerve terminals by tetrodotoxin, mu-conotoxin and reduced external sodium

Braga, M.F.M. and Anderson, A.J. and Harvey, A.L. and Rowan, E.G. (1992) Apparent block of K+ currents in mouse motor nerve terminals by tetrodotoxin, mu-conotoxin and reduced external sodium. British Journal of Pharmacology, 106 (1). pp. 91-94. ISSN 1476-5381

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Abstract

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.