WT and Mfn2 KO MEFs were co-transfected with plasmids encoding I) GFP and ER-Mfn2 or control (CT) plasmid. The effect of caffeine-induced (20 mM) ER Ca2+ release on mitochondrial Ca2+ was measured (n= 30 cells from 3 independent experiments). Data are presented as mean ± SEM 