Voltage clamp study of fast excitatory synaptic currents in bullfrog sympathetic ganglion cells.

Abstract

Excitatory postsynaptic currents (EPSCs) have been studied in voltage-clamped bullfrog sympathetic ganglion B cells. The EPSC was small, rose to a peak within 1-3 ms, and then decayed exponentially over most of its time-course. For 36 cells at -50 mV (21-23~ peak EPSC size was -6.5 • 3.5 nA (mean • SD), and the mean decay time constant 1" was 5.3 • 0.9 ms. ~" showed a small negative voltage dependence, which appeared independent of temperature, over the range -90 to -30 mV; the coefficient of voltage dependence was -0.0039 • 0.0014 mV -1 (n = 29). The peak current-voltage relationship was linear between -120 and -30 mV but often deviated from linearity at more positive potentials. The reversal potential determined by interpolation was ~-5 mV. EPSC decay T had a O~0 = 3. The commonly used cholinesterase inhibitors, neostigmine and physostigmine, exhibited complex actions at the ganglia. Neostigmine (1 • 10 -s M) produced a time-dependent slowing of EPSC decay without consistent change in EPSC size. In addition, the decay phase often deviated from a single exponential function, although it retained its negative voltage dependence. With 1 • 10 -6 M physostigmine, EPSC decay was slowed but the decay phase remained exponential. At higher concentrations of physostigmine, EPSC decay was markedly prolonged and was composed of at least two decay components. High concentrations of atropine (10 -5 to 10 -4 M) produced complex alterations in EPSC decay, creating two or more exponential components; one decay component was faster and the other was slower than that observed in untreated cells. These results suggest that the time-course of ganglionic EPSC decay is primarily determined by the kinetics of the receptorchannel complex rather than hydrolysis or diffusion of transmitter away from the postsynaptic receptors.

Analysis of current noise evoked by nicotinic agonists in rat submandibular ganglion neurones

“…The other (fast) component has a mean channel lifetime close to 9 ms at this potential. This has not generally been observed in other autonomic ganglion cells where only one population of channels has usually been found (Kuba & Nishi, 1979;MacDermott, Connor, Dionne & Parsons, 1980). Various nicotinic antagonists have been found to show some degree of selectivity between the fast and the slow components of the response (Rang, 1982).…”

Synaptic inhibition of the M‐current: slow excitatory post‐synaptic potential mechanism in bullfrog sympathetic neurones.

“…The fast e.p.s.p. is analogous to the muscle end-plate potential and likewise results from the transient opening of cation-selective channels (Nishi & Koketsu, 1960;Blackman, Ginsborg & Ray, 1963;Kuba & Nishi, 1979: MacDermott, Connor, Dionne & Parsons, 1980). The slow e.p.s.p.…”

Characteristics of the acetylcholine‐operated channel at twitch and slow fibre neuromuscular junctions of the garter snake.

“…Attempts here to induce extrasynaptic currents far from end-plates in slow fibres failed. In the following paper (Dionne, 1980) more exacting tests for extrasynaptic channels in the immediate vicinity of the slow fibre synapses are described. Neither the direct method employed here nor the indirect method described there have revealed such a population.…”