Differences in rectification between fast and slow muscle ACh-activated single-channel currents. Sample single-channel traces at holding potentials that are either positive or negative to the current reversal potential (∼0 mV) for fast muscle (A) and slow muscle (B). (C) The current–voltage relations for fast muscle synaptic currents, with each point representing the mean ± SD of seven recordings, fit by a linear curve. (D) The current–voltage relations for synaptic currents in slow muscle, with each point representing the mean ± SD for 10 recordings, fit by a second-order polynomial curve.