Hypoxia Promotes Atrial Tachyarrhythmias via Opening of ATP-Sensitive Potassium Channels

Figures

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  Figure 1.. Cardiac ATP-sensitive potassium channel (KATP) subunit RNA expression. Differential KATP subunit expression in (A) WT mice (n=16) and (B) human (data are from 3 commercially available male donors aged 49, 65, and 69 years all with normal cardiac structure and function and no medical history). Data are normalized to GAPDH and relative to atria (mice) and right atrium ([RA]; human). C, Levels of expression of Kir6.1 (Kcnj8) in Kir6.1 global knockout (6.1-gKO) relative to wild-type (WT) mice (n=3 both groups) and (D) of all KATP subunits in hearts of 6.1-gKO mice relative to WT (n=3 both groups). E, Levels of expression of Kir6.2 (Kcnj11) in Kir6.2 global knockout (6.2-gKO) relative to WT mice (n=4 both groups) and (F) of all KATP subunits in hearts of 6.2-gKO mice relative to WT (n=4 both groups). The data are shown as median, interquartile range, 5 to 95 percentile, by (A and B) 2-way ANOVA with Bonferroni posttest, (C through F) independent samples t test. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001. A indicates atria; LA, left atrium; LV, left ventricle; RV, right ventricle; and V, ventricles.

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  Figure 2.. ATP-sensitive potassium channel (KATP) current in isolated murine atrial cardiomyocytes. A, D, and G, representative time-course traces at +40 mV; B, E, and H, whole-cell current density-voltage traces; C, F, and I, summary of mean whole-cell current densities at +40 mV in isolated atrial myocytes (AMs) from wild type (WT), Kir6.1 global knockout (6.1-gKO), and Kir6.2 global knockout (6.2-gKO) mice. Current density-voltage relationships were recorded using a 1-second ramp protocol (−150 mV to +50 mV) from a holding potential of −80 mV. Summary data are shown as mean±SEM (WT, n=17–28 cells from 13 mice; 6.1-gKO, n=8-14 cells from 4 mice; 6.2-gKO, n=6-12 cells from 5 mice), by 1-way ANOVA with Dunnett posttest vs baseline and Bonferroni posttest for selected means. *P<0.05, ***P<0.001, ****P<0.0001. DZX indicates diazoxide 100 µmol/L; GLIB, glibenclamide 10 µmol/L; PIN, pinacidil 10 µmol/L; PNU, PNU37883 50 µmol/L; and TOLB, tolbutamide 100 µmol/L.

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  Figure 3.. Action potentials (APs) in isolated murine atrial cardiomyocytes. A, Overlay of wild type (WT), Kir6.1 global knockout (6.1-gKO), and Kir6.2 global knockout (6.2-gKO) APs at baseline. B, AP duration at various percentage phase of repolarization (APDx). C, Membrane potential at various percentage phase of repolarization (APDx). D through F, Representative APs at baseline and with application of the ATP-sensitive potassium channel (KATP) activator diazoxide 100 µmol/L (DZX). G through J, Effects of DZX on APD. K, Effect of DZX on resting membrane potential in atrial myocytes (AMs) from WT, 6.1-gKO and 6.2-gKO mice. Whole-cell current-clamp recordings were made to 600 pA/5 milliseconds stimulating square pulses at 1 Hz. Data are shown as mean±SEM (n cells/n mice), by (B and C) repeated measures 2-way ANOVA with Dunnett posttest vs WT, (G through I) repeated measures 2-way ANOVA with Bonferroni posttest, (J) 2-way ANOVA with Bonferroni posttest, (K) paired t test. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001.

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  Figure 4.. Atrial effective refractory period (ERP) in Langendorff mouse hearts. A, Example signal window showing final S1 and S2 beats of a drive train. The pink lines show timing of automatically detected pacing artifact followed by the induced atrial activation and electrogram. Note can be made of the large sharp local atrial signal and small far-field ventricular electrogram. B, Baseline sinus heart rate. C, Baseline ERP. D, ERP at 8 minutes of hypoxia. E, ERP change normalized to baseline during hypoxia. Data are shown as mean±SEM (n), by (B through D) 1-way ANOVA with Tukey posttest, (E) 2-way ANOVA with Dunnett posttest vs WT. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001. 6.1-gKO indicates Kir6.1 global knockout; and 6.2-gKO, Kir6.2 global knockout.

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  Figure 5.. Atrial conduction velocity (CV) in Langendorff mouse hearts. A and B, Example activation maps across the flexible microelectrode array (FlexMEA) covering the surface of the left atrial appendage. Black dots denote active electrodes and contours and color fill signify isochrones of activation. Activation times are given by the color bar legend. A, Baseline and (B) hypoxia demonstrating conduction slowing. Stimulation is adjacent to the top right electrode in each case. (C) Baseline steady-state CV (120 milliseconds coupling interval). D, Steady-state CV at 8 minutes of hypoxia. E, CV restitution at baseline. F, CV restitution at 8 minutes of hypoxia (steady state = 120 milliseconds coupling interval). G, CV change normalized to baseline during hypoxia. Data are shown as mean±SEM (n), by C and D 1-way ANOVA with Tukey posttest, (E through G) 2-way ANOVA with Dunnett posttest vs WT or baseline as indicated. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001. 6.1-gKO indicates Kir6.1 global knockout; and 6.2-gKO, Kir6.2 global knockout.

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  Figure 6.. Atrial minimum wavefront path length (WFPL) in Langendorff mouse hearts. A, Baseline WFPL. B, WFPL at 8 minutes hypoxia. C, WFPL change normalized to baseline during hypoxia. D, WFPL change normalized to baseline during hypoxia with and without tolbutamide 100 µmol/L (TOLB) ATP-sensitive potassium channel (KATP) inhibition in wild-type (WT) mice. E, As for (D) but for Kir6.1 global knockout (6.1-gKO) mice. Data are shown as mean±SEM (n), by (A and B) 1-way ANOVA with Tukey posttest, (C) 2-way ANOVA with Dunnett posttest vs WT or baseline as indicated, (D and E) 2-way ANOVA with Bonferroni posttest. *P<0.05, **P<0.01, ***P<0.001. 6.2-gKO indicates Kir6.2 global knockout.

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  Figure 7.. Kir6.2 global knockout (6.2-gKO) mice atria display reduced arrhythmia inducibility to programmed electrical stimulation (PES) during hypoxia/reperfusion. Proportions of hearts with PES-induced sustained atrial arrhythmia (500 milliseconds or longer): (A) At baseline; (B) during the hypoxia/washout 20-minute protocol; (C) 8 to 12 minutes of hypoxia with and without ATP-sensitive potassium channel (KATP) inhibition in the wild type (WT); (D) as (C) but for Kir6.1 global knockout (6.1-gKO). E, Example trace of arrhythmia induced by programmed electrical stimulation. Trace showing the final 3 beats of a drive train S1 with preceding pacing artifact, followed by the S2 with shorter coupling interval also with preceding pacing artifact, followed by atrial tachycardia (further pacing artifact is also present from the next drive train in the automated sequence), which on this occasion went on to last for 25 beats and ≈700 milliseconds. F, As for (E) but example trace of induced atrial fibrillation, which went on to last for ≈2 seconds. *P<0.05 by Fisher exact test. TOLB indicates tolbutamide 100 µmol/L.