[Excitatory effect of noradrenaline on rat airway parasympathetic ganglion neurons].

The effects of noradrenaline (NAd) on neurons acutely isolated from airway parasympathetic ganglia of rats were investigated by use of the nystatin perforaded-patch recording mode. Under current-clamp conditions, an application of 10(-6) M NAd onto the ganglion neurons evoked a depolarization which was accompanied by regenerating repetitive action potentials. NAd concentration-dependently induced inward current with decreasing membrane conductance when a ganglion neuron was held at a holding potential of -40 mV. The half-maximum effective concentration (EC50) of NAd was 1.7 x 10(-7) M, and the response was mimicked by an alpha 1-adrenoceptor agonist cirazoline and was inhibited by WB-4101, an alpha 1A-adrenoceptor antagonist. Oxymetazoline, a partial agonist for an alpha 1A-adrenoceptor, also evoked the inward current with an EC50 of 3.5 x 10(-8) M. The maximum current induced by oxymetazoline (10(-6) M) was 44% of that induced by NAd. NAd also inhibited the amplitude of M-current deactivation induced by hyperpolarizing step from a VH of -25 mV to -50 mV with an EC50 of 2.0 x 10(-4) M. These results suggest that NAd directly depolarizes the airway parasympathetic ganglion neurons of rats associated with an inhibition of M-current through the alpha 1A-adrenoceptors.