Fig. 2.

I_pe is carried by Ca²⁺ and Na⁺. A–D,I_pe was triggered by NMDA exposure (10 min, 100 μm) or intracellular perfusion of high-calcium solution. A, Responses of I_peto changes of extracellular ionic composition. Line above current traces indicates period of perfusion of 20 mm NaCl solution, 20 mm KCl solution, or 10 mm CaCl₂ solution. Changes ofI_pe reached a plateau (indication of complete solution change around cell) within 2 sec. These responses are not from the same cell; because I_pe grows over time, we chose instead to show responses in which theI_pe amplitudes (directly before the change to test solution) matched. B, C, Voltage ramps (−90 mV to +90 mV, 600 msec duration) performed 3–6 sec after changing to the indicated solutions. B,I_pe during the voltage ramp in the presence of extracellular control solution (continuous trace) and low-Cl⁻ solution (dotted trace). (Traces essentially overlap.) The reversal potentials ofI_pe were 0.8 ± 0.6 mV (control solution) and 0.8 ± 0.7 mV (low-Cl⁻ solution, mean ± SD, n = 5). C,I_pe during the voltage ramp in the presence of extracellular control (a), 10 mmCaCl₂ (b), 20 mm KCl (c), and 20 mm NaCl (d) solutions. During the voltage ramps, TTX (5 μm) and Co²⁺ (200 μm) were applied to block voltage-dependent Na⁺ and Ca²⁺ currents. Baseline leak current before NMDA exposure was not subtracted from current traces shown in B and C, because the subtraction made no significant difference in the reversal potential or conductance measured. D, Neither MK-801 (20 μm) nor Co²⁺ (200 μm) suppressed I_pe. Voltage steps (+10 mV) were applied every 25 sec. Cells examined had anI_pe smaller than −1 nA.