Non-canonical role of the sympathetic nervous system in the day–night rhythm in heart rate

Figures

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  Figure 1.. Effect of sustained β-adrenergic receptor blockade on the day–night rhythm in heart rate. (a) Mean hourly uncorrected (solid lines) and activity-corrected (dashed lines) heart rate measured by telemetry over a 24 h cycle in control and propranolol-treated mice (n = 7 or 8 per group). (b) Activity-corrected heart rates measured by telemetry during the day (12 h light period) and night (12 h dark period) in control and propranolol-treated mice (n = 6–8 per group). (c) Activity-corrected heart rates measured over 1 h by telemetry at ZT 6 and ZT 12 in control and propranolol-treated mice (n = 6–8 per group). (d) Mean fast Fourier transform of the heart rate (not activity-corrected) from control and propranolol-treated mice over at least 48 h (n = 6 per group). Inset shows details of the transform at the lowest frequencies (dotted line shows a frequency of 1 per 24 h). (e) Amplitude of the 1 per 24 h component of the fast Fourier transform in control and propranolol-treated mice (n = 6 per group). (f) Ex vivo beating rate measured by extracellular potential recording in right atrial preparations isolated at ZT 0 and ZT 12 from control (n = 9 or 10 per time point) and…

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  Figure 2.. Heat maps of transcripts that retained (both), lost (control) or gained (propranolol) rhythmicity in the sinus node after sustained β-adrenergic receptor blockade. Mean expression of transcripts showing a day–night rhythm (confirmed by JTK_CYCLE) in both control and propranolol-treated mice or just control or propranolol-treated mice is shown at ZT 0, 6, 12 and 18 (n = 4 or 5 per measurement). Expression is colour-coded according to the Z-score (deviation from the mean measured in terms of s.d.) and goes from red (low expression) to green (high expression). Transcripts in each section are ordered by the time of peak expression (LAG value from JTK_CYCLE). Heatmaps constructed using the online tool heatmapper.ca without clustering. (Online version in colour.)

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  Figure 3.. Expression of sinus node clock transcripts and transcripts for clock-controlled transcription factors across the 24 h cycle in control and propranolol-treated mice. In this and similar figures, transcript expression is shown at ZT 0, 6, 12 and 18 in control and propranolol-treated mice (n = 4 at ZT 0 for the control mice; otherwise n = 5 for each time point and group); expression at ZT 0 is replotted at ZT 24 as a visual aid. Data (shown as means ± s.e.m.) are normalized to the ZT 0 mean in control mice. In the case of transcripts showing a significant day–night rhythm (as determined by JTK_CYCLE), the data are fitted with a sine wave shown as a solid line. In the case of transcripts not showing a significant day–night rhythm, the data are fitted with a sine wave to guide the eye, but it is shown as a dotted line. The adjusted p-value (from JTK_CYCLE) and R2 value (measure of the goodness of fit of the sine wave to the mean data; from GraphPad Prism version 9) for the control and propranolol-treated conditions are shown. (Online version in colour.)

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  Figure 4.. Expression of sinus node ion channel and Ca2+-handling transcripts across the 24 h cycle in control and propranolol-treated mice. In all cases, the transcripts show a significant day–night rhythm in control but not propranolol-treated mice. (Online version in colour.)

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  Figure 5.. Expression of transcripts for sinus node-specific and ubiquitous transcription factors across the 24 h cycle in control and propranolol-treated mice. (Online version in colour.)

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  Figure 6.. Evidence that the suppression of the day–night rhythm in heart rate in propranolol-treated mice is the result of the loss of the day–night rhythm in HCN pacemaker ion channels. (a) In vivo heart rate (not activity-corrected) measured by ECG telemetry after intraperitoneal injection of the HCN blocker ivabradine (6 mg kg−1) at ZT 0 and ZT 12 in control (n = 3 or 4 per time point) and propranolol-treated (n = 5 or 7 per time point) mice. Baseline average heart rate at ZT 0 and ZT 12 was calculated for 1 h over several days. In the case of ivabradine (iva), heart rate was calculated as the mean over 30 min starting 10 min after the injection at ZT 0 and ZT 12. Time-dependent differences were tested for statistical significance using a two-way ANOVA with Tukey's multiple comparisons test. (b) Effect of ivabradine on the heart rate at ZT 0 and ZT 12 in control and propranolol-treated mice. From the same data as (a). (c) Beating rate of the sinus node isolated from control and propranolol-treated mice at ZT 0 and ZT12 after block of the funny current, If, by 2 mM Cs+ (n = 5–10 per time point and group). Differences were tested for statistical significance using a two-way ANOVA with…