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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 8. — Recovery of resting heart rate in isolated WT and Girk4^−/− hearts and time course of ACh-induced heart rate reduction under continuous ISO perfusion. (A, left) Basal heart rate (HR) recovery in 0.3 µM ACh after application of 0.1 µM ISO for 5 min in WT (n = 8; closed circles) and Girk4^−/− (n = 7; open circles) Langendorff-perfused hearts. The first data point for each genotype represents heart rate under basal condition, whereas the second data point is the averaged maximal heart rate under ISO, before switching to the solution containing ACh. Dashed lines indicate the basal heart rate before ISO perfusion in WT (black) and Girk4^−/− (gray) mice. Continuous lines represent fitting of experimental data points for calculating τ_r of recovery. Averaged τ_r for WT and Girk4^−/− isolated hearts is shown in the insets. (right) Sample ECG traces from WT and Girk4^−/− recorded in isolated hearts under resting conditions (before ISO) and 35 s after ACh application. Note that at 35 s in Girk4^−/− but not in WT hearts, the pacing rate was still higher than at rest. (B) Similar to A, the first data point is the averaged maximal heart rate with ISO before perfusion. The time course (τ_r) of rate reduction was calculated during combined perfusion of 0.1 µM ISO and ACh 0.3 µM after maximal stimulation of pacing by ISO in WT (n = 8; closed circles) and Girk4^−/− (n = 6; open circles) hearts. The inset shows averaged τ_r for WT and Girk4^−/− hearts. Error bars represent SEM. Statistical symbols: *, P < 0.05.