Fig. S4.

(Related to Fig. 5) M7Vs do not sequester Ca²⁺ or Mg²⁺. (A) M7Vs isolated from SV40MES-13 cells were loaded with Fluo4-AM (A) or MagFluo4 (B) and were perfused with the indicated concentrations of Ca²⁺ or Mg²⁺. Then, 5 µM Bromo-A23187 in 1 mM EDTA was used to deplete cations at the end of the time course. (C and D) HEK293 cells coexpressing GCaMP6s in the intravesicular loop of TRPM7 (green) and ER-targeted (RCEPIAer, red, C) or cytosolic (R-GECO1, red, D) Ca²⁺ sensors were stimulated with 100 µM ATP in HBSS. ATP-induced vesicular Ca²⁺ spikes (C and D, green) and synchronous Ca²⁺ efflux from the ER (C, red) or influx into the cytosol (D, red) were monitored simultaneously. Traces are representative of at least three experiments.