Influence of sex on intracellular calcium homeostasis in patients with atrial fibrillation

Aims

Atrial fibrillation (AF) has been associated with intracellular calcium disturbances in human atrial myocytes, but little is known about the potential influence of sex and we here aimed to address this issue.

Methods and results

Alterations in calcium regulatory mechanisms were assessed in human atrial myocytes from patients without AF or with long-standing persistent or permanent AF. Patch-clamp measurements revealed that L-type calcium current (I_Ca) density was significantly smaller in males with than without AF (−1.15 ± 0.37 vs. −2.06 ± 0.29 pA/pF) but not in females with AF (−1.88 ± 0.40 vs. −2.21 ± 0.0.30 pA/pF). In contrast, transient inward currents (I_Ti) were more frequent in females with than without AF (1.92 ± 0.36 vs. 1.10 ± 0.19 events/min) but not in males with AF. Moreover, confocal calcium imaging showed that females with AF had more calcium spark sites than those without AF (9.8 ± 1.8 vs. 2.2 ± 1.9 sites/µm²) and sparks were wider (3.0 ± 0.3 vs. 2.2 ± 0.3 µm) and lasted longer (79 ± 6 vs. 55 ± 8 ms), favouring their fusion into calcium waves that triggers I_TIs and afterdepolarizations. This was linked to higher ryanodine receptor phosphorylation at s2808 in women with AF, and inhibition of adenosine A_2A or beta-adrenergic receptors that modulate s2808 phosphorylation was able to reduce the higher incidence of I_TI in women with AF.

Conclusion

Perturbations of the calcium homoeostasis in AF is sex-dependent, concurring with increased spontaneous SR calcium release-induced electrical activity in women but not in men, and with diminished I_Ca density in men only.

Treatment with beta-blockers normalizes RyR2 phosphorylation and calcium spark activity in atrial myocytes from patients with atrial fibrillation

Background

Atrial fibrillation has been associated with an increase in ryanodine receptor (RyR2) phosphorylation and local calcium release (calcium sparks). Carvedilol, a nonselective beta-adrenergic receptor blocker also inhibits the cardiac ryanodine receptor (RyR2), but it has been suggested that the enantiomer R-carvedilol only inhibits RyR2 activity and hence has the potential to inhibit calcium sparks without affecting RyR2 phosphorylation.

Purpose

This study aimed to determine the ability of the enantiomers R- and S-carvedilol to reverse RyR2 phosphorylation at s2808 and calcium sparks induced by the β2-adrenergic agonist fenoterol, in order to determine the relationship between RyR2 phosphorylation at s2808 and calcium spark frequency, and to assess the efficacy of R- and S-carvedilol.

Methods

Human right atrial myocytes were isolated and subjected to immunofluorescent labelling of total and s2808 phosphorylated RyR2, or loaded with fluo-4 and subjected to confocal calcium imaging. Beta-adrenergic receptors were first activated with 3μM fenoterol and then inhibited by different concentrations of carvedilol R- or S-enantiomers.

Results

Incubation of myocytes with fenoterol increased the s2808/RyR2 ratio from 0.32±0.03 to 0.66±0.05 (n=18, p<0.001). Incubation with 0.1, 0.3, 1 or 3μM R-carvedilol in the presence of fenoterol changed the s2808/RyR2 ratio to 0.64±0.05, 0.44±0.04, 0.34±0.07 and 0.28±0.05 (p<0.01) respectively. For comparison 3μM S-carvedilol reduced the s2808/RyR2 ratio to 0.23±0.06 in myocytes from 5 patients (p<0.01). Confocal calcium imaging revealed that fenoterol increased the spark density from 0.28±0.04 to 1.24±0.25 events/s/1000μm2 (n=9, p<0.01) and addition of 0.1, 0.3, or 1μM R-carvedilol changed the frequency to 1.32±0.52, 0.38±0.05, and 0.15±0.05 events/s/1000μm2 (p<0.01) respectively. Analysis of atrial myocytes from patients without atrial fibrillation revealed that the s2808/RyR2 ratio was similar in 25 patients treated with beta-blockers (0.39±0.04) and 57 that did not receive beta-blockers (0.44±0.03, p=0.33) while the s2808/RyR2 ratio was significantly smaller in 16 patients with atrial fibrillation receiving beta-blockers (0.43±0.08) than in 5 patients that did not (0.80±0.19, p<0.05).

Conclusions

R-carvedilol reverses the effects of beta-adrenergic stimulation on s2808 phosphorylation and calcium sparks in human atrial myocytes, and treatment with beta-blockers reduces excessive RyR2 phosphorylation at s2808 in patients with atrial fibrillation to levels observed in those without the arrhythmia, pointing to beta-adrenergic receptors as a target for controlling RyR2 phophorylation and activity in atrial fibrillation.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Science and Innovation & Spanish Ministry of Health and Consume

Pathological phosphorylation of the ryanodine receptor at s2808 increases the number of individual clusters activated per calcium spark and the calcium released per cluster

Background

Atrial fibrillation (AF) has been associated with an increase in ryanodine receptor (RyR2) phosphorylation and local calcium release (sparks), but it is not known how calcium dynamics of individual RyR2 clusters affect spark dimensions and properties.

Purpose

This study aimed to test the hypothesis that pathological alterations in the phosphorylation of individual RyR2 clusters at s2808 facilitate the fusion of spontaneous calcium release events from neighboring RyR2 clusters.

Methods

Cardiomyocytes from mice with GFP-tagged RyR2 or human right atrial tissue were subjected to confocal calcium imaging or immunofluorescent labelling of total and s2808 phosphorylated RyR2. Calcium signals were measured at a frame rate of 240 Hz in a 0.5 x 0.5 μm region of interest (ROI) for each GFP-tagged RyR2 cluster and spontaneous calcium release events were detected using a custom-made algorithm.

Results

Calcium sparks recorded in 41 myocytes with GFP-tagged RyR2s was due to the spontaneous opening of a single RyR2 cluster in 91.2±2.2% of the cells and two neighbouring clusters in (6.2±1.6%) of the cells. Events with two clusters had bigger amplitude (0.14±0.01 vs. 0.10±0.01, p<0.05), were wider (1.43±0.03 vs. 1.13±0.04 μm, p<0.05), and lasted longer at half maximum (59.8±5.2 vs. 44.4±2.4 ms, p<0.01). Consequently, the calcium spark mass, measured as the time integral of the spark in each ROI increased from 9.2±1.6 for 1 cluster to 17.8±3.5 a.u. for 2 clusters (p<0.01). Interestingly, sparks lasted longer (79±5 vs. 61±4 ms, p<0.001) were wider (3.0±0.2 vs. 2.2±0.1 μm, p>0.001) and had bigger mass (31.5±3.3 vs. 21.9±3.3 a.u, p<0.01) in atrial myocytes from 21 patients with AF than in 27 without. Because phosphorylation of RyR2 clusters at s2808 (s2808/total RyR2) was higher in patients with than without AF (0.80±0.19 vs. 0.44±0.03, p<0.05), we tested how stimulation of RyR2 phosphorylation at s2808 with the β2-adrenergic agonist fenoterol (3μM) affected calcium release in individual RyR2 clusters. Fenoterol increased s2808 phosphoryaltion from 0.39±0.05 to 0.79±0.16 (p<0.05, n=9). It also increased the mass of sparks with 1 RyR2 cluster (from 9.2±1.1 to 16.0±2.3 a.u., p<0.01) and sparks with 2 clusters from 17.8±3.5 to 23.6±2.7 a.u. Moreover, it increased the fraction of sparks with 2 clusters from 6.2±1.6% to 19.3±3.3% (p<0.01) and sparks with 3 clusters reached 6.3±1.9% in the presence of fenoterol.

Conclusions

The calcium spark mass recorded in patients without AF is comparable to that recorded during activation of calcium release from one or two GFP-tagged RyR2 clusters. The larger mass and slower kinetics of sparks recorded in patients with AF is compatible with an increase in the calcium released from each RyR2 cluster and a 3-fold increase in sparks with 2 or 3 RyR2 clusters observed in GFP-tagged RyR2s when phosphorylation at s2808 is increased to levels observed in atrial fibrillation.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Science and Innovation; Generatlitat de Catalunya

P3830Carvedilol treatment diminishes spontaneous calcium release and electrical activity in human atrial myocytes

Background

Atrial fibrillation (AF) has been associated with an increase in spontaneous calcium release induced electrical activity, which could potentially be reversed by carvedilol, a nonselective beta-blocker that also inhibits the cardiac ryanodine receptor (RyR2). Interestingly the enantiomer R-carvedilol inhibits the RyR2 but not beta-adrenergic receptors, allowing it to effectively prevent calcium release-induced spontaneous electrical activity without inducing bradycardia and hypotension.

Purpose

The purpose of this study was to determine how carvedilol treatment affects calcium release-induced transient inward currents (ITI) in human atrial myocytes from patients with AF; and to test the effects of R-carvedilol on spontaneous calcium release in order to assess its therapeutical utility.

Methods

Human atrial myocytes were isolated from patients undergoing cardiac surgery and subjected to patch-clamp technique (n=60) or confocal calcium imaging (n=6). Beta-2 adrenergic receptors were activated with the selective agonist fenoterol (3μM) and 1μM R-carvedilol was used to inhibit spontaneous calcium release events.

Results

Recordings of calcium release-induced transient inward currents (ITI) revealed that carvedilol treatment reduced the ITI frequency in patients with AF from 2.2±0.4 events/min in untreated patients to 0.59±0.35 events/min (p<0.01), which was even lower than the incidence in patients without AF (1.0±0.1 events/min; p<0.01). To assess the effects of R-carvedilol, myocytes were first simulated with fenoterol. This increased the calcium spark frequency from 23±15 to 960±336 events/s/1000μm2 in 16 cells from 6 patients (p<0.05). This was due to an increase in the spark site density (from 0.50±0.24 to 12.1±2.4 sites/1000μm2, p<0.001) rather than in the firing rate (0.068±0.14 vs. 0.035±0.012 sparks/s in control, p=0.14). Fenoterol also increased the spark duration from 50.9±5.4 to 77.3±4.1ms (p<0.001) without affecting the amplitude. Importantly, fenoterol also induced global calcium release events such as calcium waves and transients (2.8±1.1 vs. 0 events/min in control, p<0.05). When R-carvedilol was added, the effects of fenoterol were abolished, reducing the incidence of calcium sparks to 69±51 events/s/1000μm2 (p<0.05), the spark site density to 1.68±1.04 sites/1000μm2 (p<0.01), the spark duration to 63.4±4.3ms (p<0.05), and calcium waves and transients were reduced to 0.21±0.14 events/min (p<0.05).

Conclusions

Carvedilol treatment reduces the ITI frequency in patients with AF to levels below that observed at baseline in patients without AF. Furthermore, the non-beta-blocking R-carvedilol enantiomer abolishes spontaneous calcium release events induced by beta-2 adrenergic stimulation in human atrial myocytes, proposing a therapeutical utility for this compound in patients with AF linked to excessive spontaneous calcium release.

Acknowledgement/Funding

SAF2017-88019; Marato2015-20-30; SGR2017-1769; CIBERCV

Automated analysis of single cells using Laser Tweezers Raman Spectroscopy

In recent years, significant progress has been made into the label-free detection and discrimination of individual cancer cells using Laser Tweezers Raman Spectroscopy (LTRS). However, the majority of examples reported have involved manual trapping of cells, which is time consuming and may lead to different cell lines being analysed in discrete batches. A simple, low-cost microfluidic flow chamber is introduced which allows single cells to be optically trapped and analysed in an automated fashion, greatly reducing the level of operator input required. Two implementations of the flow chamber are discussed here; a basic single-channel device in which the fluid velocity is controlled manually, and a dual-channel device which permits the automated capture and analysis of multiple cell lines with no operator input. Results are presented for the discrimination of live epithelial prostate cells and lymphocytes, together with a consideration of the consequences of traditional 'batch analysis' typically used for LTRS of live cells.