(A–D) All experiments were performed in 293FT cells. Fluorescence with excitation at 485 nm was normalized to that of untreated cells. Shown are time courses of fluorescence response of FrexH-and cpYFP-expressing cells when 100 μM pyruvate (A) or 1 mM lactate (C) was added to the cell culture medium in the absence of glucose and time courses of fluorescence response of Frex-Mit- and cpYFP-Mit-expressing cells when 1 mM pyruvate (B) or 1 mM lactate (D) was added to the cell culture medium in the absence of glucose.
(E) Dose-dependent response of cytosolic NADH level to different concentration of lactate, as measured by Frex and FrexH fluorescence.
(F) AOA blocked the lactate-induced increase of mitochondrial NADH as measured by fluorescence of Frex-Mit 30 min after addition of lactate to the cell culture medium in the absence of glucose. Error bars represent SEM. See also Figure S5.