Figure 7.

Recovery of resting heart rate in Girk4^−/− mice. (A and B) After swimming test (A) and upon intraperitoneal injection of ISO (B). (A, left) Swimming test (5 min) was used to monitor heart rate (HR) during physical exercise of WT (n = 5; closed circles) and Girk4^−/− (n = 6; open circles) mice. Continuous lines represent fitting of experimental data points to calculate τ_r of recovery. Dashed lines represent the basal heart rate before swimming test in WT (black) and Girk4^−/− (gray) mice. Averaged τ_r for WT and Girk4^−/− mice is reported in the insets. (right) Samples ECG traces from WT and Girk4^−/− mice at rest (before swimming) and 85 min after swimming. Note that at 85 min in Girk4^−/− but not in WT mice, heart rate was still higher than the heart rate in the resting condition. (B, left) Basal heart rate recovery after direct activation of β-adrenergic receptors by 0.1 mg/kg ISO in WT (n = 15; closed circles) and Girk4^−/− (n = 11; open circles) mice. Dashed lines represent the basal heart rate before injection of ISO in WT (black) and Girk4^−/− (gray) mice. Averaged τ_r for WT and Girk4^−/− mice is reported in the inset. (right) Samples ECG traces from WT and Girk4^−/− mice under basal conditions and 60 min after ISO injection. At min 60 in Girk4^−/− mice but not in WT, heart rate was still higher than the basal heart rate. Error bars represent SEM. Statistical symbols: *, P < 0.05.