Effect of the IP3R ligand-binding domain on mitochondrial Ca2+ uptake. (A and C) HeLa cells were transfected with mitochondrially targeted (mtAEQmut; top) and cytosolic aequorin (bottom). Control traces are shown in black; traces from cells cotransfected with the IP3R-LBD224-605 (A) and the IP3R-LBD224-605 K508 mutant (C) are shown in gray. Traces are representative of >15 experiments from >5 preparations. (B) Effect of the cytosolic-, OMM-, and ER-targeted IP3R-LBD224-605 on peak mitochondrial and cytosolic Ca2+ responses (top and bottom, respectively). (D) Effect of the OMM-IP3R-LBD224-605 (K508A), the IP3-binding PH domain of the p130 PLC-like protein (OMM-p130-PH), and the OMM targeted N-terminal (1-604 aa) part of the IP3R (OMM-IP3R-LBD1-604), on mitochondrial (top) and cytoplasmic Ca2+ responses (bottom) after 100 μM histamine stimulation. Data in B and D were normalized to mean of the control group. Mean ± SEM of variation is shown as percentage. Cells were transfected, and [Ca2+] was measured as described in Materials and methods. Values are shown. *, P < 0.05; **, P < 0.01. For absolute values see Table S1, available at http://www.jcb.org/cgi/content/full/jcb.200608073/DC1.