Synaptic inhibition of the M‐current: slow excitatory post‐synaptic potential mechanism in bullfrog sympathetic neurones.

Abstract

Slow muscarinic excitatory post-synaptic currents (slow epsc) generated by preganglionic nerve stimuli were recorded in voltage-clamped bullfrog sympathetic neurons. IM-an outward, voltage-dependent, K+-current-was inhibited during the slow epsc, and membrane conductance was reduced in a voltage-dependent manner. The slow epsc was associated with reduced outward rectification in the steady-state current-voltage (I/V) curve at membrane potentials more positive than -60 mV, with no change in the shape of the non-rectifying part of the I/V curve at more negative potential. The amplitude of the slow epsc was reduced by membrane hyperpolarization, to zero at membrane potentials equal to, or more negative than, -60 mV. The voltage sensitivity of the slow epsc accorded with that of IM. The slow epsc results from a selective inhibition of IM.