H) Determination of ER Ca2+. WT and Mfn2 KO MEFs were transfected with plasmid encoding the ER-located Ca2+ sensor LAR-GECO1. After 48 h, fluorescence was recorded every 3 seconds. ER Ca2+ release was induced with caffeine (20 mM) as indicated (n= 30 cells from 3 independent experiments). Data are presented as mean ± SEM. 