Activation of mGluR I suppresses Kir currents in Müller cells. A, DHPG (10 μm), a selective mGluR I receptor agonist, inhibited remarkably and reversibly Kir currents. The currents were evoked by a series of pulses from a holding potential of −80 mV to −160 mV in −20 mV increments. The I–V relationships show voltage-dependent reduction in Kir current amplitudes. n = 10. B, Plot of Kir inward currents evoked by a voltage step from a holding potential of −80 mV to −160 mV as a function of time, showing that DHPG (10 μm) significantly suppressed the Kir current amplitudes. n = 6. The representative current traces (top) are taken from the time points as indicated. C, Internal dialysis of GDP-β-S (3 mm) prevented the DHPG-induced suppression of Kir currents. The representative current traces (top) are used to generate the plot. n = 5. D, Plot of Kir inward currents as a function of time, showing that preperfusion of MPMQ (10 μm) failed to block DHPG-induced reduction in Kir current amplitudes. n = 6. The representative current traces (top) are taken from the time points as indicated. E, Plot of Kir inward currents as a function of time, showing that preperfusion of MPEP (10 μm) blocked DHPG-induced reduction in Kir current amplitudes. n = 5. The representative current traces (top) are taken from the time points as indicated. All the current amplitudes are normalized to the amplitude of the first evoked event.