Fig. 1.

PDC blocked glutamate uptake in Müller cells isolated from the newt retina. A, Glutamate (1 mm) was puff applied (100 msec; timing indicated as thebar at the top) to a Müller cell that was whole-cell voltage-clamped at various potentials (noted on theleft). The glutamate-induced uptake current did not reverse its polarity at positive potentials. B,I–V curves obtained in the presence of 1 mmglutamate (Glu) and 200 μm PDC. Membrane currents were measured by applying voltage ramps (130 mV/300 msec). Each I–V curve was derived from the difference between the average of three current traces in the presence and absence of the chemicals, which were applied via the Y-tube microflow system.C, The uptake currents induced by various concentrations (top) of glutamate (Glu) or PDC. Bothtraces were obtained from the same cell voltage-clamped at −75 mV. D, Dose–response curves for glutamate (top panel) or PDC (bottom panel). Means ± SEM are illustrated (pooled data from 16 cells). Data points were fitted by the Michaelis–Menten equation. E, Inhibition of the glutamate-induced uptake current by PDC (200 μm). The concentration of glutamate (Glu) was 200 μm (left andmiddle) and 1 mm (right). The cell was held at −75 mV. F, Estimation of the uptake rate of glutamate in the presence of PDC. A simple competitive inhibition model was used with the values ofK_Glu and K_PDCobtained in D. The concentration of PDC is shown at theright of the curves.