The amplitude of miniature end-plate currents (MEPCs) and end-plate currents generated by iontophoresis of acetylcholine (ACh) were recorded in voltage-clamped toad sartorius fibres. Single channel conductance was determined from analysis of current fluctuations. In normal solution, but even more so in solutions containing lithium instead of sodium, both the peak conductance during a miniature end-plate current and the conductance of individual end-plate channels varied with membrane potential, becoming less at more hyperpolarized potentials. Single channel conductance was not influenced by membrane potential in solutions containing potassium or caesium instead of sodium. It was concluded that the nature of the ions passing through an end-plate channel influences its conductance.
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