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. 2013 Aug;142(2):113–126. doi: 10.1085/jgp.201310996

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© 2013 Mesirca et al.

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Figure 6. — Heart rate in Girk4^−/− mice. (A) Sample traces of ECGs recorded in freely moving WT and Girk4^−/− mice. (B and C) Dot plots of beat to beat variability (in bpm) of heart rate (HR) of WT (B) and Girk4^−/− (C) mice for a 5-min ECG recording epoch. The dashed lines indicate the averaged heart rate. (D and E) Bar graphs showing averaged low-frequency (LF; D) and high-frequency (HF; E) power spectra of HRV in WT (n = 10) and Girk4^−/− (n = 9) mice for recordings shown in B and C. (F) Histogram showing the distribution of normalized averaged heart rates in a 24-h period of telemetric ECG recordings in WT (n = 10; black line) and Girk4^−/− (n = 9; gray line) mice. For a given mouse, individual heart rate values were calculated every 20 s over the 24-h recording and then normalized to the maximal heart rate recorded for the mouse to allow comparison between WT and Girk4^−/− animals. Note that the two distributions have similar shapes, but that Girk4^−/− heart rates are shifted toward higher values. (G) Relationship between heart rate and spontaneous home cage activity (rate to activity relationship) of WT (closed bars) and Girk4^−/− mice (open bars). Activity values are defined as arbitrary units (A.U.) and have been binned in six intervals of increasing activity. Binning was adjusted to obtain maximal resolution of the heart rate to activity relationship. (H) Similarity in the range of heart rate regulation as a function of activity in WT and Girk4^−/− mice. For each animal, the heart rate corresponding to bin 1 (lowest activity) was subtracted from the heart rate recorded at other degrees of activity. (I) Averaged heart rate measured over a 24-h recording in Girk4^−/− (583 ± 11 bpm; n = 9; open bars) and WT mice (539 ± 10 bpm; n = 10; closed bars; P < 0.05). (J) Range of heart rate regulation calculated from the differences between the maximum and minimum heart rate in each mouse recorded over the 24-h recording period. Error bars represent SEM. Statistical symbols: *, P < 0.05; **, P < 0.01; ***, P < 0.001; and ****, P < 0.0001.