Properties of active K-ATP channels in (wv/wv) dopaminergic SN neurons. A,Current responses of a (wv/wv) dopaminergic SN neuron to voltage ramps from −120 to −40 mV from a holding potential of −60 mV in the presence of 100 μm QX-314 and in 100 μm QX-314 + 100 μm tolbutamide as indicated. B, Tolbutamide-sensitive current obtained by subtraction of traces in A. Dotted linesindicate zero levels. C, Dose–response curve for tolbutamide-inhibition of whole-cell currents in (wv/wv) dopaminergic SN neurons. Filled squares represent means of six separate experiments. Vertical lines indicate SEM. The line represents the fit of the mean data by Hill equations with an IC₅₀ of 6.9 μm and a Hill coefficient of 0.9.