Effects of membrane potential and temperature on the excitatory post-synaptic current in the crayfish muscle

1. Effects of membrane potential and temperature on the excitatory post-synaptic current (e.p.s.c.) were studied in the voltage-clamped crayfish muscle. E.p.c. was recorded either by measuring the feedback current through an intracellular wire electrode or by focal recording with an extracellular micro-electrode. 2. The amplitude of the e.p.s.c. obtained by the voltage clamp method varied almost linearly with membrane potential between -100 mV and +70 mV, whilst the reversal potential was +23.8 +/- 3.9 mV (S.E. of mean). 3. The declining phase of the extracellular e.p.s.c. was slightly prolonged by depolarization and shortened by hyperpolarization. Potential dependence of the decay time constant was expressed by tau = a exp (AV), with a = 2.78 msec and A = 0.0037 mV-1. 4. The decay time constant had a Q10 of 2.3 and the growth time had a Q10 of 1.5. 5. The voltage dependence of the decay phase of the e.p.s. was the reverse of that found in frog end-plate. It is concluded that the voltage dependence of the time course is not related either to the charge of ions which carry the synaptic current or to the charge of the transmitter.