Fig. 4. Chelating intracellular calcium decreased the late phase of plateau potentials. A, In control conditions, the neuron responded to a 3 sec pulse of depolarizing current with an accelerating discharge, followed by an afterdischarge (A1, A3, filled circles). Application of the calcium chelator BAPTA-AM (50 μm) did not change the initial response of the neuron (A3, open circles) but interrupted the acceleration of discharge after 1.5 sec (A3,dashed line) and abolished the afterdischarge (A2). A3, Instantaneous frequency plot calculated as in Figure 1 for the discharges recorded inA1 and A2. B, In control conditions, a long-lasting and intense plateau potential was triggered by a short current pulse (1 sec) in another DHN (B1). Note the slow increase in firing frequency during the afterdischarge. In the presence of BAPTA-AM, the duration and intensity of the afterdischarge gradually decreased (B2, 40 min), until it disappeared (B3, 1 hr 40 min). Conversely, the firing frequency during the 1 sec stimulation did not change (C, instantaneous frequency plot calculated forB1–B3). Under the same conditions, a weak afterdischarge could be triggered by a shorter pulse of current (B4). All the recordings were obtained in the presence of the mGluR agonist 1S,3R-ACPD (25 μm).A, B, Different neurons.