(A) Fractional enrichment of m2 α-ketoglutarate and m2 succinate in retinas supplied with 5 mM U-13C-glucose for 0.02, 0.5, 1, 2, 5, 15, 30, and 60 min (n = 3 to 7 retinas per time point; error bars indicate SEM). (B) Fractional enrichment of m1 fumarate and m1 succinate in retinas supplied with 5 mM 4-2H-glucose for 0.02, 0.5, 1, 2, 5, 15, 30, and 60 min (n = 3 retinas per time point; error bars indicate SEM). (C) Fractional enrichment of m4 fumarate and m4 succinate in retinas supplied with 5 mM 12C-glucose + 50 μM U-13C-malate for 0.02, 5, 15, 30, and 60 min (n = 3 to 5 retinas per time point; error bars indicate SEM). (D) Graphical description of observed (top) and maximal (bottom) contributions of oxidative TCA cycle activity and reverse SDH activity to maintaining the retinal succinate pool.