Muscarinic agonists block five different potassium conductances in guinea-pig sympathetic neurones.

Muscarinic excitation of sympathetic ganglion cells has usually been thought to result from inhibition of an outward K+ current, the M current, although in other neurones several conductances have been shown to be blocked by muscarinic agonists. We report that, as well as resting K+ conductance, all of four different K+ conductances, two voltage-dependent (M currents and A currents) and two calcium-dependent (responsible for slow and very slow afterhyperpolarizations), present in different sub-types of guinea-pig sympathetic neurones, are inhibited by the muscarinic agonists, bethanechol and muscarine. All of these effects increase neurone excitability and can lead to repetitive discharge.