Figure 2. Effect of mibefradil (green traces) and Ni²⁺ (blue traces) on Ca²⁺ and Na⁺ currents in dissociated STN neurons.

The holding potential is –120 mV. (A) Representative currents show that 3 μM mibefradil dramatically inhibits the Ca²⁺ current elicited at –60 mV (left panel) but has little inhibitory effect on that elicited at +30 mV (middle panel) in the same neuron. The peak LVA Ca²⁺ current amplitude (elicited at –60 mV) in the presence of drug is normalized to that in control to give the average inhibitory effect of 1–10 μM mibefradil (right panel, n = 4). Scale bars: 20 pA/20 ms. (B) 300 μM Ni²⁺ and 3 μM mibefradil lack an effect on subthalamic neuronal Na⁺ currents that are either elicited at 0 mV (and abolished by 300 nM TTX; left panel) or elicited at –40 mV (middle panel). In this experiment, the external TEA-based solution is replaced by a low-calcium Tyrode’s solution (see Methods). The Na⁺ current (elicited at 0 mV) in the presence of drug is normalized to that in control to show the average drug effects (right panel, each n = 4). The dashed line indicates zero current level. Scale bars: 500 pA/0.5 ms. (C) Inhibition of LVA Ca²⁺ currents by 300 μM Ni²⁺ and 3 μM mibefradil with the addition of 300 nM TTX in the external TEA-based solution. The normalized Ca²⁺ current to the control is plotted to show the averaged effects (right panel, n = 4). The box shows the same inhibition of LVA currents by Ni²⁺ and mibefradil if 5 mM Ca²⁺ is replaced by 5 mM Ba²⁺ in the external TEA-based solution. Scale bars: 50 pA/20 ms.