Fig. 4.

ER-localized TriPer responds optically to exogenous H₂O₂. a Fluorescent photomicrographs of live COS7 cells, co-expressing TriPer^ER and PDI-mCherry as an ER marker. b Time course of in vivo fluorescence excitation (488/405 nm) ratiometric images (R^488/405) of HyPer^ER or TriPer^ER from cells exposed to H₂O₂ (0.2 mM) for the indicated time. The excitation ratio in the images was color coded according to the map shown. c Plot showing the dependence of in vivo fluorescence excitation (488/405 nm) ratio of TriPer^ER on H₂O₂ concentration in the culture medium. d Bar diagram of excitation ratio of TriPer^ER from untreated (UNT) cells, cells exposed to H₂O₂ (0.2 mM, 15 min), or cells 15 min after washout (H ₂ O ₂ ➔WO) (mean ± SEM, n = 12). e A ratiometric trace of TriPer^ER expressed in RINm5F cells exposed to H₂O₂ (0.2 mM) followed by bovine catalase for the indicated duration. f A ratiometric trace of TriPer^ER expressed alone or alongside ER catalase (CAT ^ER) in RINm5F cells exposed to increasing concentrations of H₂O₂ (0–0.2 mM). Shown are representatives of n ≥ 3