Fig. 4: Characterization of eLACCO1.1 in live mammalian cells.

a Representative images of eLACCO1.1 and control biosensor deLACCO expressed on cell surface of HeLa cells before and after 10 mM L-lactate stimulation. Similar results were observed in more than 10 cells. Scale bars, 10 μm. b Box plots of l-lactate-dependent ΔF/F for eLACCO1.1 and deLACCO, and ΔR/R for eLaconic. n = 26, 28 and 13 cells for eLACCO1.1, deLACCO and eLaconic, respectively. c Photobleaching curves (left) and time constants (right) for EGFP, cpGFP and eLACCO1.1 expressed on the cell surface. To test photostability, we continuously illuminated eLACCO1.1-expressing cells using one-photon wide-field microscopy. n = 25, 24 and 23 cells for EGFP, cpGFP and eLACCO1.1, respectively. In the photobleaching curves, solid lines represent mean value and shaded area represent s.d. One-way ANOVA, P > 0.05. d Time-course of the fluorescence response of eLACCO1.1 on cell surface under l-lactate stimulation. To examine the on-rate kinetics of eLACCO1.1, we bathed eLACCO1.1-expressing HeLa cells in a solution containing 10 mM l-lactate. The plot was fitted with a single exponential function. n = 13 cells (mean ± s.e.m.). e In situ titration of l-lactate on HeLa cells. Data were fitted with Hill equation. n = 11 cells (mean ± s.e.m.). f Representative images of eLACCO1.1 expressed in primary cortical neurons before and after 10 mM l-lactate stimulation. eLACCO1.1 was expressed at relatively high levels, as indicated by bright membrane-localized fluorescence with some puncta apparent. Similar results were observed in more than 10 neurons from three independent experiments. Scale bars, 10 μm. In the box plots in b, c, the narrow part of notch with the horizontal line is the median; the top and bottom of the notch denote the 95% confidence interval of the median; the top and bottom horizontal lines are the 25th and 75th percentiles for the data; and the whiskers extend one standard deviation range from the mean represented as black filled circle. Source data of b–e are provided as a Source Data file.