Muscarinic receptors mediating suppression of the M-current in guinea-pig olfactory cortex neurones may be of the M2-subtype.

Guinea-pig olfactory cortical neurones in vitro were voltage clamped by means of a single intracellular microelectrode technique. Hyperpolarizing voltage commands from holding potentials between -40 to -50 mV produced slow inward current relaxations reflecting deactivation of the M-current (IM). IM was reversibly suppressed by 30 microM muscarine or carbachol; this suppression was insensitive to pirenzepine (up to 300 nM) but was inhibited by gallamine (10-20 microM) or 4-diphenyl-acetoxy-N-methylpiperidine (100, 500 nM), suggesting the involvement of the M2-type muscarinic receptor.