Maximum relative fluorescence change (ΔF/F%) of sweet neuron responses stimulated by sugar/bitter compound mixtures with or without acid in tarsi of flies expressing the inward-rectifying potassium channel Kir2.1 (Gr64f-LexA, Gr33aGAL4/LexAop-GCaMP3.0,UAS-Kir2.1; black bars). Silencing of the bitter neuron has little or no effect on de-repression; Controls are Gr64f-LexA/LexAop-GCaMP3.0,UAS-Kir2.1 (white bars); den, denatonium. lob, lobeline. quin, quinine. ΔF/F(%), maximum relative fluorescent change before and after tastant application.