Dose dependence and ryanodine sensitivity of the caffeine-evoked reduction in glutamate release. A, The effect of caffeine (filled bars) versus control (open bars) on release was observed at 5 mm(2.14 ± 0.14 vs 4.37 ± 0.35 control) and 10 mm(1.96 ± 0.23 vs 4.67 ± 0.41 control) caffeine but not with 1 mm caffeine (2.86 ± 0.22 vs 2.64 ± 0.19 in control). B, Ryanodine (20 μm) had no effect on glutamate release from reduced retinas under normal conditions or when depolarized by KCl (20 mm). Data are normalized to the average of the control samples (open bars). In the presence of ryanodine, 10 mm caffeine still suppressed glutamate release by 42.5%.