Activation of M2 muscarinic receptors causes an alteration of action potentials by modulation of Ca entry in isolated sympathetic neurons of rabbits.

Activation of muscarinic receptors caused an alteration of the configuration of action potentials in the isolated sympathetic ganglion cells of rabbits, e.g. elimination of the shoulder in the falling phase and depression of the afterspike-hyperpolarization and after-depolarization. The responsible receptors appeared to be of the M2-type since the above changes by the low concentration (greater than or equal to 10 nM) of muscarinic agonists were potently antagonized by AF-DX 116. Similar changes were induced by removing the external Ca2+ and no more changes were produced by further application of muscarinic agonists in the absence of external Ca2+. The action potential in sympathetic neurons is thus shown to be modulated via the M2 receptor possibly by regulating the Ca entry.