Figure 5.

DA modulates Na⁺ current measured from nucleated patches. A, Application of DA caused a small increase in the peak I_Na. B, DA (gray) caused a leftward shift in the voltage of activation of I_Na, without a significant change in the inactivation. C, The effects of DA were mimicked by a D₂ agonist quinpirole (10 μm). A D₁ agonist, SKF81297 (10 μm), exerted the opposite effect, decreasing Na⁺ currents. D, To test whether I_Na was modulated within the limited voltage ranges examined in current-clamp recordings (above), I_Na was evoked with a 10 mV step to −55 mV, grossly mimicking the depolarization evoked by summation of EPSPs at depolarized membrane potentials. The peak amplitude of this I_Na was greatly enhanced by DA. Overlayed are averaged traces of the current evoked by a 10 mV step to −55 mV (black) and to −80 mV (gray) for comparison. E, DA also prolonged the decay time of a Na⁺ current evoked by a voltage step from −100 mV to approximately −60 mV. All I_Na traces depicted are averages of 5–10 sweeps. *p < 0.05, significant difference in a paired t test comparison between baseline and DA conditions.