Fig. 2.

The major presynaptic ionic currents. Representative currents evoked by depolarizing steps of voltage from a holding potential of −70 mV to −30, −10, +10, +30, and +50 mV are shown. A, Presynaptic currents evoked before (left) and after (right) application of 300 nm tetrodotoxin (TTX). Similar results were seen in six other preparations. B,Left, Presynaptic currents in TTX; right, after addition of 1 mm 3,4 diaminopyridine (DAP). Note that at higher voltages (see values given next to the traces) the current does not increase linearly with potential. A and B were taken from different varicosities. Internal solution B was used. Similar results were obtained in four other preparations.