Voltage-clamp analysis of peptidergic slow depolarizations in bullfrog sympathetic ganglion cells.

1. The membrane currents during the late slow excitatory post-synaptic potential (late slow e.p.s.c.s) and luteinizing hormone-releasing hormone (LHRH)-induced depolarization of nicotinized and atropinized bullfrog lumbar sympathetic ganglion cells were studied with voltage-clamp methods. 2. Two types of late slow e.p.s.c. were observed. The Type I response was associated with a decreased conductance and was depressed by membrane hyperpolarization. The Type II response was accompanied by an increased conductance and was augmented by membrane hyperpolarization. 3. LHRH also induced two types of responses. The nature of the LHRH-induced current and the late slow e.p.s.c. in each neurone was similar, if not identical. 4. The Type I response appeared to be produced primarily by a suppression of the M current (Brown & Adams, 1980) and partially by a depression of the resting K+ conductance. The Type II response is probably due to an increased conductance to Na+ or Na+ and some other cations.