Muscarine-induced hyperpolarization in rat dosolateral septal nucleus neurons in vitro

The direct effect of muscarine on neurons of the rat dorsolateral septal nucleus (DLSN) was examined by using conventional microelectrode and single-electrode voltage-clamp techniques. Muscarine (1-50 mu M) caused a hyperpolarization accompanied by an increase of a voltage-independent potassium conductance. Pirenzepine competitively antagonized the muscarine-induced hyperpolarization with an apparent dissociation constant (Kd) value of 54 nM. The Kd values for AF-DX 116 and methoctramine were 410 nM and 380 nM, respectively. Furthermore, intracellular loading with GTP gamma S, a non-hydrolyzable GTP analog, blocked irreversibly the muscarine-induced hyperpolarization. In addition, pretreatment of neurons with pertussis toxin (PTX) prevented the hyperpolarization produced by muscarine. These results suggest that muscarine hyperpolarizes DLSN neurons via a voltage-independent potassium conductance by acting at M(4) subtype receptors which are coupled to a PTX-sensitive G-protein in DLSN neurons.