Fig. 6. Rat-1 luminescence rhythms as measured by three different recording systems. Rat-1/PerLuc4-43 cells were prepared as described in Materials and Methods. (A and B) Hamamatsu H6240 system: cells grown in a 35-mm dish were stimulated for 2 h with 10 mM forskolin, and then the medium was replaced with 2 ml of DMEM/B27 medium. (B) An expanded ordinal scale of the same data shown in A. (C) Taylortron. Cells grown on a 15-mm coverslip were treated for 2 h with 10 mM forskolin, and transferred to a 20-ml scintillation vial containing 1.5 ml of DMEM/B27 medium. (D) PolarStar. Cells grown in a 24-well plate were stimulated for 2 h with 10 mM forskolin, and the medium was changed to 1 ml of DMEM/FBS medium per well. Time 0 = onset of stimulation. Temperatures were as follows: Taylortron and PolarStar at 36.0ºC, Hamamastu H6240 at 36.5ºC. Luminescence is plotted as counts per measurement time interval, which is different for each apparatus, and therefore the intensities are not directly comparable. For each apparatus, three separate representative traces are shown.