Zn2+ potentiates and inhibits neuronal nAChRs. A, Current responses of an α4β2-expressing oocyte to 10 μm ACh before, during, and after coapplication of 70 μm(top trace) or 1 mm Zn2+(bottom trace). Calibration: 60 nA, 20 sec.B, Current responses of an α3β2-expressing oocyte to 4 μm ACh before, during, and after coapplication of 70 μm Zn2+(top trace) or 1 mm Zn2+(bottom trace). Calibration: 300 nA, 20 sec. C, Current responses of an α4β4-expressing oocyte to 1 μm ACh before, during, and after coapplication of 100 μm Zn2+(top trace) or 3 mm Zn2+(bottom trace). Calibration: 200 nA, 20 sec.