AMPAR activation increases both (Ca2+)i and (Zn2+)i. levels. A, B. Time course of Ca2+ and Zn2+-dependent changes in fura-2 fluorescence upon activation of AMPARs: Neuronal cultures loaded with fura-2 were imaged before, during, and after a 1 min exposure to 300 µM kainate. After the kainate challenge, neurons were washed for 30 min in a physiological buffer either at pH 7.4 (A) or pH 6.2 (B). At the end of the washout period, neurons were exposed for 5 min to the cell permeant Zn2+ chelator TPEN (20 µM). Traces show mean fura-2 AF (expressed as % over baseline of 340/380 nm ratios) (±SEM) of 13–24 neurons from one experiment representative of 5–6, respectively.