NMDA receptor-induced current entry dominates within the oscillation range.

<p><b>A.</b> Oscillations were induced in whole-cell current clamp in a ventral horn neuron (100 µM NMDA, 1 µM TTX) from a recently transformed animal. The average plateau potential in this neuron was −60 mV. <b>B</b> The recording mode was switched to voltage clamp in the same cell as A. TEA (5 mM) and 4-AP (1 mM) were added to the solution. A step protocol (10 mV increments from a holding potential of −90 mV) shows the voltage-gated Ca²⁺ current in NMDA (black, 100 µM), following NMDA washout and exchange of Ca²⁺ (2.6 mM) for Ba²⁺ (grey, 2.6 mM). NMDA (100 µM) was then reapplied with Ba²⁺ present (blue). <b>C</b> Average I-V plot of voltage-gated currents for Ba²⁺ (grey), Ba²⁺+NMDA (100 µM, blue) and Ca²⁺+NMDA (100 µM, black). Red line and red traces denote −40 mV, the average peak of membrane potential oscillations. Error bars express ± SEM.