Figure 1. Synaptic transmission during voltage clamp of a presynaptic terminal. (a) to (c) Experimental data: top trace, presynaptic voltage; middle trace, postsynaptic response; lower trace, calcium current. The S-shape of the current onset can be seen at 60 mV depolarization from a holding potential of –70 mV. Note the fast tail current and the ‘on’ and ‘off ’ excitatory postsynaptic potential (EPSP). (d) to (f) Numerical solutions to the mathematical mode: traces as in (a) to (c). C. Recorded EPSP [Ca²⁺]₀ = 10 mmol L^–1. Figure modified from Llinás (1999).

Figure 2. Dependence of calcium current (a) and EPSP (b) on presynaptic depolarization. (a) Solid circles, steady state I_Ca; open circles, tail current. (b) Solid circles, ‘on’ EPSP; crosses, ‘off ’ EPSP. The continuous curves show solutions of the mathematical model [Ca²⁺]₀ = 10 mmol L^–1. On the Pre-V axis, 0 corresponds to a holding potential of –70 mV. Figure modified from Llinás (1999).

Figure 3. Synaptic delay. (a) The ‘on’ response is shown for a 60 mV presynaptic voltage clamp; 733 s latency. (b) The ‘off ’ response is seen following a voltage clamp to the suppression potential (140 mV); 200 s latency. (c) and (d) EPSPs generated by the mathematical model for a 60 mV clamp (‘on’ response latency, 675 s), and a 140 mV clamp (‘off ’ response latency, 150 s). (e) Histogram showing the variation in latency observed for the ‘on’ response (mean 0.894 ± 0.168 ms, n = 51), and the ‘off ’ response (mean 0.192 ± 0.27 ms, n = 25). Figure modified from Llinás (1999).