Fig. 1.

The presynaptic voltage control method shows that accelerated release during facilitation is not associated with a change in the presynaptic Ca²⁺ transient. Simultaneously recorded IPSPs (A), Ca²⁺transients (B), and presynaptic voltage steps (C) are displayed on the same time scale. Control (dotted line) and facilitated (solid line) recordings are superimposed. The inset inA illustrates the protocol used to activate F2 facilitation (see Results for details). The time courses of presynaptic voltage steps with (solid line) or without (dotted line) preceding conditioning stimuli are identical, whereas that of facilitated IPSP (A,solid line) is accelerated. Meanwhile, Ca²⁺ transients activated by control and test steps (B) are also superimposable. This experiment was performed in the presence of 1 mm 4-AP, 40 mmTEA, and 100 nm TTX. Each represents the average of 30 trials. This experiment was performed at 15°C.