Figure 4. I_bkg and I_Cl,ir have different sensitivities to Zn²⁺ blockade.

The voltage protocol is shown above B; this experiment is typical of 5 cells. A-C, current traces recorded from an isolated Xenopus RPE cell in Ringer solution (A) and in Ringer solution containing 10 μm (B) or 300 μm (C) Zn²⁺. D, current-voltage relationship of the instantaneous current at the onset of the hyperpolarizing pulse (I_bkg) in 0 (▪), 3 μm (•), 10 μm (○), 30 μm (▾) and 1 mm (♦) Zn²⁺. E, current-voltage relationship for I_Cl,ir tail currents recorded at +100 mV in 0 (▪), 10 μm (○), 100 μm (▴), 300 μm (▾), and 1 mm (♦) Zn²⁺. Virtually identical results were obtained if the time-dependent inward current rather than tail current amplitude was used as a measure of I_Cl,ir. F, inhibition of I_bkg and I_Cl,ir by Zn²⁺. I_bkg and I_Cl,ir in different [Zn²⁺] were normalized to the control current in the absence of Zn²⁺.