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

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Abstract
1. Slow muscarinic excitatory post‐synaptic currents (slow e.p.s.c.s) generated by preganglionic nerve stimuli were recorded in voltage‐clamped bullfrog sympathetic neurones. 2. IM‐‐an outward, voltage‐dependent, K+‐current‐‐was inhibited during the slow e.p.s.c., and membrane conductance was reduced in a voltage‐dependent manner. 3. The slow e.p.s.c. was associated with reduced outward rectification in the steady‐state current‐‐voltage (I/V) curve at membrane potentials more positive than‐‐60 m V, with no change in the shape of the non‐rectifying part of the I/V curve at more negative potential. 4. The amplitude of the slow e.p.s.c. was reduced by membrane hyperpolarization, to zero at membrane potentials equal to, or more negative than, ‐60 m V. The voltage sensitivity of the slow e.p.s.c. accorded with that of IM. 5. It is concluded that the slow e.p.s.c. results from a selective inhibition of IM.