[Na⁺] changes detected by FLIM of CoroNaGreen: (A) Top: FL images of CoroNaGreen-AM-loaded HEK cells under control conditions (ACSF) and in response to perfusion with glucose-free saline containing sodium azide (NaN₃; 5 mM) and 2-desoxyglucose (2-DG; 1 mM) for 2 min. Each image was collected for a period of 80 s. The first image was taken in ASCF (“T80”), before exposing the cells to the metabolic inhibitors (red bars) and generating three more images (“T160, T240, T320”). Bottom: [Na⁺] at each time point (mean ± SEM; n = 24) in the three compartments. Dotted line represents baseline [Na⁺] in the respective compartment. (B) Same experimental setup and illustration as in A, showing the effect of perfusion with nominally K⁺-free saline for 1 min (indicated by green bar; n = 17). (A and B) Scale bars, 20 µm. *, P < 0.05, **, P < 0.01, and ***, P ≤ 0.001.