G. Schematic representation of EATR assay: eGFP fluorescence, but not mCherry, is lost at acidic pH. Chondrocytes with indicated genotypes (ctrl=wild type) were treated with FGF18 (50 ng/mL; 12 hours) and BafA1 (200 nM; 3 hours) where indicated. ER acidification was measured by FACS. Mean +/- standard error of the mean (sem) of N=3 biological replicates. Analysis of variance one way (ANOVA) p<0.0001; Tukey's post hoc test ***p<0.0005; **p<0.005; NS not significant. 