Fig. 1.

Suppression of outward K⁺ currents by activating D2 receptors in rat RGCs. A Representative outward K⁺ currents recorded from an RGC, showing that extracellular application of quinpirole (10 μmol/L), a selective D2 receptor agonist, significantly suppressed the current amplitudes. The cell was held at −70 mV and the currents were evoked by a series of voltage pulses (from −70 mV to +30 mV in increments of 10 mV). B, CI-V curves showing that quinpirole voltage-dependently suppressed average peak (B) and steady-state (C) current amplitudes (n = 12). ^**P < 0.01, ^***P < 0.001 vs control. D Time course of quinpirole-induced suppression of K⁺ currents at +30 mV. Note that the current amplitudes were almost unchanged during a period of 8 min without quinpirole (Control), while quinpirole significantly reduced the current amplitudes. E, F Concentration-dependent suppression of peak (E) and steady-state (F) current amplitudes by quinpirole (n = 7–11 for each quinpirole concentration). G Sample current traces showing that sulpiride (10 μmol/L), a selective D2 receptor antagonist, blocked the quinpirole-induced suppression of K⁺ currents recorded in a rat RGC. Bar chart summarizing the changes of K⁺ current amplitudes at +30 mV under different conditions (n = 11). All data are normalized to control and presented as the mean ± SEM.