Structural and electro-anatomical characterization of the equine pulmonary veins: implications for atrial fibrillation

INTRODUCTION/OBJECTIVES

Spontaneous pulmonary vein (PV) activity triggers atrial fibrillation (AF) in humans. Although AF frequently occurs in horses, the origin remains unknown. This study investigated the structural and electro-anatomical properties of equine PVs to determine the potential presence of an arrhythmogenic substrate.

ANIMALS, MATERIALS AND METHODS

Endocardial three-dimensional electro-anatomical mapping (EnSite Precision) using high-density (HD) catheters was performed in 13 sedated horses in sinus rhythm. Left atrium (LA) access was obtained retrogradely through the carotid artery. Post-mortem, tissue was harvested from the LA, right atrium (RA), and PVs for histological characterization and quantification of ion channel expression using immunohistochemical analysis.

RESULTS

Geometry, activation maps, and voltage maps of the PVs were created and a median of four ostia were identified. Areas of reduced conduction were found at the veno-atrial junction. The mean myocardial sleeve length varied from 28 ± 13 to 49 ± 22 mm. The PV voltage was 1.2 ± 1.4 mV and lower than the LA (3.4 ± 0.9 mV, P < 0.001). The fibrosis percentage was higher in PV myocardium (26.1 ± 6.6 %) than LA (14.5 ± 5.0 %, P = 0.003). L-type calcium channel (CaV1.2) expression was higher in PVs than LA (P = 0.001). T-type calcium channels (CaV3.3), connexin-43, ryanodine receptor-2, and small conductance calcium-activated potassium channel-3 was expressed in PVs.

CONCLUSIONS

The veno-atrial junction had lower voltages, increased structural heterogeneity and areas of slower conduction. Myocardial sleeves had variable lengths, and a different ion channel expression compared to the atria. Heterogeneous properties of the PVs interacting with the adjacent LA likely provide the milieu for re-entry and AF initiation.

Endo- and epicardial mapping of spontaneous ventricular fibrillation during acute myocardial infarction in a porcine model

Introduction

Ventricular fibrillation (VF) during the first minutes of acute myocardial infarction (AMI) is among the most frequent causes of sudden cardiac death. Albeit mechanisms for arrhythmogenesis during ischemia are well understood on a cellular level, little is known in an in-vivo setting.

Aim

Aim of this study was the development and characterization of a porcine model of AMI and spontaneous VF with continuous electrical mapping using a non-contact mapping system (EnSite Array) in the left ventricle (LV) and an electrode sock covering the whole heart. Activation-recovery intervals (ARI), beat-to-beat variation in repolarization (BVR), and ectopic activation were measured.

Methods

Nineteen Danish Landrace pigs (56±4 kg, heart weight 251±20 g) were anaesthetized, equipped with electrophysiological (EP) catheters in the coronary sinus, right and LV as well as a multi electrode array (St. Jude, EnSite Array) catheter in the LV. Thoracotomy was performed and the sock electrode was placed on the pericardium covering the anterior and the posterior surface of the heart. Finally, the mid-left anterior descendent artery was occluded with a percutaneous transluminal coronary angioplasty balloon to induce AMI and kept in place for 45 minutes followed by 20 minutes of reperfusion. Data from both systems were analyzed offline using a custom-made software.

Results

All pigs had stable hemodynamic parameters during the procedure. Spontaneous VF occurred in 8/19 pigs during the occlusion period. Epi- and endocardial mapping showed similar shortening of ARI in the infarcted area (Figure 1A). AMI shortened ARI in the ischemic area to a greater extend in pigs that developed VF (Figure 1B) and caused beat-to-beat variation in repolarization (BVR) in later phases (Figure 1C). Ectopic beats proceeding spontaneous VF varied in activation site and subsequent repolarization (Figure 1D, left). Multiple short-coupled ectopic beats destabilized the electrical substrate further and led to progressive ARI shortening (Figure 1D, last 4 beats).

Conclusion

We present the first whole heart mapping experiments of spontaneous VF during AMI with endo- and epicardial mapping. Pigs with VF had shorter ARI, greater dispersion but similar BVR during AMI compared to those without VF. These findings provide a deeper understanding of arrhythmogenesis during AMI and can help to develop new antiarrhythmic drugs or to assess risk factors of VF.

Funding Acknowledgement

Type of funding sources: None.

Sympatho-vagal activation during obstructive respiratory events in pigs and blunted atrial arrhythmogenic effects by pharmacological IKACh-inhibition

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo nordisk foundation

Background

Obstructive sleep apnea (OSA) is associated with a sympatho-vagal activation which is suspected to create a complex substrate for atrial fibrillation (AF).

Purpose

In pigs, we investigated atrial arrhythmogenic consequences of simulated obstructive respiratory events by intermittent negative upper airway pressure (INAP) application and tested antiarrhythmic properties of an atria-specific IK,ACh-inhibitor.

Methods

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds, every 10 minutes, three times before (vehicle) and two times following infusion of an IK,ACh-inhibitor. P-wave, PQ-duration, atrial effective refractory periods (AERP) and left ventricular hemodynamic parameters (maximum upstroke velocity, minimal downslope velocity and systole duration) were acquired before (Pre-INAP), during (INAP) and after (Post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol.

Results

During vehicle infusion, INAP transiently shortened AERP (Pre-INAP: 147±8ms vs. Post-INAP 105±12 ms; p=0.021) and increased AF-inducibility (Pre-INAP: 10±6% vs. Post-INAP 57±15%; p=0.018). Whereas p-wave duration remained stable, PQ-duration prolonged (Pre-INAP: 130±6ms vs. Post-INAP 142±7ms; p=0.03). Left ventricular maximum upstroke velocity increased (Pre-INAP: 1990±118 mmHg/s vs. Post-INAP 3980±704 mmHg/s; p=0.04), minimal downslope velocity decreased and systole duration shortened (Pre-INAP: 236±6 ms vs. Post-INAP 202±12 ms; p=0.04).

The IK,ACh-inhibitor increased AERP (vehicle 147±8ms vs. IK,ACh-inhibitor 171±9ms; p=0.05) and sufficiently prevented INAP-associated AERP-shortening (Pre-INAP: 171±9ms vs. Post-INAP 180±9ms; p=0.219) and PQ-duration prolongation (Pre-INAP: 116±8ms vs. Post-INAP 113±7ms; p=0.76). INAP-induced changes of left ventricular maximum upstroke/minimal downslope velocity and systole duration remained unaffected in the presence of the IK,ACh-inhibitor.

Conclusion

During obstructive respiratory events simulated by INAP in pigs, left ventricular hemodynamic changes demonstrated elevated sympathetic tone, while atrial electrophysiological parameters resemble elevated parasympathetic tone at the same time. This was associated with increased AF-susceptibility. Pharmacological IK,ACh-inhibition blunted INAP-induced impairment of atrial electrophysiology without affecting left ventricular hemodynamic changes. Hence, pharmacological IKACh-inhibition may constitute a promising treatment strategy in AF-patients with OSA.

Pharmacological inhibition of SK-channels with AP14145 prevents atrial arrhythmogenic changes in a porcine model for obstructive respiratory events

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): This work was supported by the Novo Nordisk Foundation (Tandem Programme; #31634).

Background

Obstructive sleep apnea (OSA) creates a complex substrate for atrial fibrillation (AF), which is refractory to many clinically available pharmacological interventions.

Purpose

To investigate atrial antiarrhythmogenic properties and ventricular electrophysiological safety of small-conductance Ca2+ -activated K+ (SK)- channel inhibition in a porcine model for obstructive respiratory events.

Methods

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds, every 10 minutes, three times before and three times during infusion of the SK-channel inhibitor AP14145. Atrial effective refractory periods (AERP) were acquired before (Pre-INAP), during (INAP) and after (Post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol. For the purpose of drug safety, ventricular arrhythmicity was evaluated by heart rate adjusted QT-interval duration (QT-paced) and electromechanical window (EMW) calculation.

Results

During vehicle infusion, INAP transiently shortened AERP (Pre-INAP: 135±10 ms vs. Post-INAP 101±11 ms; p=0.008) and increased AF-inducibility. QT-paced prolonged during INAP (Pre-INAP 270±7 ms vs. INAP 275±7 ms; p=0.04) and EMW shortened progressively throughout INAP and Post-INAP (Pre-INAP 80±4 ms; INAP 59±6 ms, Post-INAP 46±10 ms). AP14145 prolonged baseline AERP, partially prevented INAP-induced AERP-shortening and reduced AF-susceptibility. AP14145 did neither alter QT-paced (Pre-AP14145 270±7 ms vs. AP14145 268±6 ms, p=0.83) nor INAP-induced QT-paced prolongation, but blunted Post-INAP associated EMW-shortening.

Conclusion

In a pig model for obstructive respiratory events, the SK-channel-inhibitor AP14145 prevented INAP-associated AERP-shortening and AF-susceptibility without impairing ventricular electrophysiology. Hence, SK-channels may represent a promising target for OSA-related AF.

Regulation of APD and force by Na+/Ca2+ exchanger in hiPSC-cardiomyocytes

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): BMBF

Introduction

Human induced pluripotent stem cell-derived cardiomyocytes (HiPSC-CM) are an emerging, powerful tool to study human cardiac physiology, pharmacology and toxicology, to model cardiovascular diseases or even to use for cardiac repair. Understanding the similarities and differences between hiPSC-CM and adult human cardiomyocytes is critical for their use. Here we focus on sodium calcium exchanger (NCX) who plays a crucial role in the Ca2+-homeostasis in the mammalian heart. Importantly, alterations in NCX expression in human heart are associated with various cardiac pathologies such as heart failure or arrhythmias. In order to investigate whether hiPSC-CM could serve as model for adult human heart NCX we measured the properties of NCX in hiPSC-CM and human ventricular tissue. Rat ventricular tissue was used for comparison.

Methods

HiPSC-CM were differentiated from a healthy iPSC line and dissociated from engineered heart tissue (EHT). Adult human and rat cardiomyocytes were digested from ventricular samples. We measured NCX current by the whole-cell patch clamp technique at 37 °C. Standard sharp microelectrodes were used to record action potentials (AP). Contractile force in human and rat ventricular samples was measured isometrically. A video-optical contractility test system was used to measure force in EHT. SEA0400 (10 µM) was used to block NCX.

Results

NCX currents could be measured in every hiPSC-CM. The NCX current densities in hiPSC-CM were larger than in human ventricular cardiomyocytes (3.2±0.2 pA/pF n=28 vs. 1.3±0.2 pA/pF n=15, p&lt;0.05), but lower than reported for rat left ventricular cardiomyocytes using the same protocol. SEA0400 shortened APD90 markedly in EHT (264.1±24.9 ms to 191±31.6 ms, n=4) and to a lesser extent in rat ventricular tissue (54.4±3.9 ms to 48.9±4.2 ms, n=7). Shortening in human left ventricular preparations was tiny (320±22.1 ms to 305.5±20.3 ms, n=6) and not different from time-matched controls (TMC). Resting membrane potential, action potential amplitude and upstroke velocity were not affected neither in EHT nor in left ventricular preparations (rat and human). Force was significantly increased by NCX block in rat ventricle (by 31±5.4%, n=18) and EHT (by 20.8±3.9%, n=4), but in human left ventricular preparations there was only a tendency to attenuate spontaneous run-down (-3.7±4.3% n=8 with SEA vs. -6.2±3.7% n=12 in TMC).

Conclusion

HiPSC-CM possess NCX in the physiological range. HiPSC-CM show NCX-effects on APD and force as predicted from rat ventricle and in full accordance with cardiac physiology. Lack of NCX effect in human adult ventricles that had been already reported previously needs further investigations.

Differential effects of positive and negative upper airway pressure application on atrial electrophysiology: implications for CPAP-therapy in OSA-patients

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo nordisk foundation

Background

Obstructive sleep apnea (OSA) is closely associated with atrial fibrillation (AF) and OSA-treatment by continuous positive airway pressure (CPAP) is believed to reduce the AF burden in OSA-patients. While negative upper airway pressure during obstructive respiratory events have been shown to increase AF susceptibility, atrial electrophysiological effects of positive upper airway pressure during CPAP-therapy are unknown.

Purpose

In pigs, we investigated differential atrial electrophysiological effects of increasing levels of CPAP-applications compared to obstructive respiratory events.

Methods

In sedated and spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds with a 10 minute resting period in-between. After four INAP-applications, during which atrial electrophysiological responses to INAP were recorded, continuous positive airway pressure was applied in increasing pressure stages for a duration of 20 minutes for each pressure level (4, 8, 12 and 16 mbar). Atrial effective refractory periods (AERP) were recorded at the free wall of the right atrium (RA) and in the distal area of the coronary sinus (CS) before (Pre-INAP), during (INAP) and after (Post-) INAP and every 10 minutes throughout the stepwise increase of CPAP.

Results

AERP shortened due to INAP application in the RA (Pre-INAP 134±7ms vs. INAP 95±7ms; p=0.008, Fig.1.), but not in the CS (Pre-INAP 132±8ms vs. INAP 110±9ms; p=0.144, Fig.2). Stepwise increases of CPAP-application up until 12 mbar did neither result in changes of RA- nor CS-AERP. Only CPAP-application at 16 mbar (CPAP16) resulted in transiently shortened CS-AERP (CPAP-baseline 140±6ms versus CPAP16 115±10ms; p=0.0081, Fig.2.), but not RA-AERPs (p=0.31, Fig.1.).

Conclusion

While simulation of obstructive respiratory events by INAP were reproducibly associated with a predominantly right atrial shortening of refractoriness, high-pressure CPAP-application of 16 mbar was associated with an isolated moderate shortening of left atrial refractoriness. These findings may have important implications for CPAP treatment in patients with AF, which should be considered in the design of future clinical studies.

Left ventricular mass quantification by echocardiography; a novel accurate and more reproducible 2D-method validated by cardiac magnetic resonance in humans and cardiac autopsy in pigs

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): The research fund of The Heart Center at Rigshospitalet, Denmark

Background

Left ventricular mass (LVM) is a strong independent risk factor for adverse cardiovascular events, but conventional echocardiographic methods used to assess and monitor individuals are currently limited by poor reproducibility and accuracy.

Purpose

We aimed to develop and validate an echocardiographic method for LVM-quantification that is simple, reproducible and accurate.

Methods

Our ‘novel method’ (Figure) adds the left ventricular wall thickness (t) to the left ventricular end-diastolic volume acquired by endocardial tracings using the biplane method of discs. For development of the novel method, cardiac assessment was performed using echocardiography followed immediately by gold standard cardiac magnetic resonance (CMR) in 85 humans with different left ventricular geometries, ranging from patients with various cardiac disorders (n = 41) to individuals without known cardiac disorders (n = 44). We compared the novel two-dimensional (2D) method to various conventional one-dimensional (1D) and 2D methods as well as three-dimensional (3D) echocardiography. Validation against anatomical LVM by cardiac autopsy was performed in thirty-four Danish Landrace pigs, weight 47-59 kg. Echocardiography was performed during anaesthesia, the pigs were euthanised, the heart explanted, and cardiac autopsy was performed where the left ventricle was trimmed and weighed for autopsy LVM.

Results

In humans, the novel method had better reproducibility in intra-examiner (coefficients of variation (CV) 8.6% vs. 11.0-14.5%) and inter-examiner analysis (CV 9.0% vs. 10.2-19.6%) than any other method, including 3D (CV intra-examiner 14.3%, inter-examiner 16.6%). Accuracy of the novel method against CMR was similar to 3D (mean difference ± 95% limits of agreement, CV): Novel: 2 ± 50g, 15.4% vs. 3D: 2 ± 51g, 15.6%; and better than the 1D-method by Devereux (7 ± 76g, 23.0%). Feasibility for the novel method was 95%. Autopsy validation in pigs confirmed high reproducibility; intra-examiner (CV 8.7% vs. 9.1-11.4%) and inter-examiner-analysis (CV 8.7% vs. 8.8-10.0%). Accuracy of the novel method against autopsy LVM was better than for the conventional echocardiographic methods: Novel -1 ± 20g, 7.8% vs. Devereux 26 ± 37g, 11.3%. 3D-validation was not available in pigs.

Conclusions

The novel 2D-based method for LVM-quantification had better reproducibility than any other echocardiographic method. Accuracy was similar to 3D and better than any conventional method. Autopsy validation in pigs supported our findings amongst the human population. As endocardial tracings using the biplane method forms part of the standard echocardiographic protocol, the novel method can easily be integrated into any echocardiographic software without substantially increasing analysis time, and provides an equivalent yet simpler alternative to 3D echocardiography. Abstract Figure.

Glucagon-like peptide-1 directly increases heart rate and shortens atrial refractoriness: an in vivo and ex vivo study in pigs

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo Nordisk Foundation Synergy program Novo Nordisk Foundation Center for Basic Metabolic Research

Background

 Treatment with glucagon-like peptide-1 receptor agonists (GLP-1 RAs) in patients with type 2 diabetes not only reduces hyperglycaemia, but also improves cardiovascular outcomes. However, GLP-1 RA treatment also increases heart rate: an apparent paradox.

Purpose

 Whether the heart rate increase is a direct effect, and whether GLP-1 affects other aspects of cardiac electrophysiology, remain unclear. To answer these questions we investigated the effect of GLP-1 infusion on cardiac electrophysiology in vivo and ex vivo in pigs and pig hearts, respectively, during sinus rhythm and pacing.

Methods

 Anaesthetised pigs (n = 8) received infusions of GLP-1 (10 pmol/kg/min). Electrocardiogram, atrial monophasic action potentials and atrial conduction velocity data were collected and atrial and ventricular effective refractory periods (ERP) were measured. For the ex vivo studies, pig hearts (n = 7) were excised, retrogradely perfused and exposed to consecutive bolus perfusions of 2 and 4 nmol GLP-1, 100 nmol of the GLP-1 receptor antagonist exendin-9-39 and a final 4 nmol bolus of GLP-1. The same electrophysiological parameters were measured.

Results

 In anaesthetised pigs, GLP-1 increased heart rate, cardiac output and diastolic pressure, while systemic vascular resistance was decreased. Infusion of GLP-1 decreased PQ interval in sinus rhythm (P = 0.019, n = 8) and during atrial pacing (P = 0.027, n = 6) with 8 ± 3 % and 12 ± 3 %, respectively. Additionally, GLP-1 decreased atrial ERP at all pacing cycle lengths (P = 0.04, n = 7), while ventricular ERP was unaffected (P = 0.29, n = 7). In the isolated perfused heart, GLP-1 increased heart rate with 13 ± 2 bpm (P = 0.001, n = 7). This increase in heart rate was completely abolished by pre-administration of exendin-9-39. Atrial ERP shortened after GLP-1 perfusion (P = 0.01, n = 7) comparable to the in vivo studies, with an average decrease of 11 ± 2 %. This effect was also abolished by exendin-9-39.

Conclusion

 GLP-1 increases heart rate through activation of the GLP-1 receptor in the isolated perfused heart, suggesting a direct effect of GLP-1 rather than activation through the central nervous system. Additionally, GLP-1 affects atrial electrophysiology, but not ventricular electrophysiology, in vivo and ex vivo independent of the increase in heart rate.

Longitudinal change in cardiac structure and function following acute coronary syndrome stratified by culprit coronary artery lesion site

Funding Acknowledgements

Type of funding sources: None.

Background

Acute coronary syndrome (ACS) has adverse consequences for the myocardium and subsequent cardiac function and structure. No reports exist comparing the differences in impact of culprit coronary artery lesion site on longitudinal remodeling and changes left ventricular structure and function.

Method

A total of 299 ACS patients treated with PCI were included in the present study. All patients had two echocardiographic examinations performed. The first was performed median 2 (IQR: 1; 3) days following PCI, while the second was performed median 240 (IQR: 81; 881) days after the first. Patients were grouped based on culprit coronary artery lesion (left anterior descending artery (LAD), right coronary artery (RCA) and circumflex artery (Cx)). Patients with multiple lesions were excluded from the present study. Univariable linear regression analysis was utilised to assess the association between culprit coronary artery lesion site and longitudinal change in cardiac structure and function.

Results

Mean age was 63 ± 11 years and 77% were male. At follow-up, mean left ventricular ejection fraction was 42 ± 9% and global longitudinal strain (GLS) was -13 ± 4%. Culprit coronary artery lesion was allocated as follows; 168 ACS patients were treated in LAD, 95 patients were treated in RCA, and 36 patients were treated in Cx. In the linear regression analysis, LAD patients displayed a greater improvement in GLS (b =-0.116, p = 0.048) compared to the two other lesion sites. LAD patients had the poorest GLS at both baseline and follow-up echocardiography (Figure). RCA lesions were associated with the largest decrease in left atrial maximum volume (LAVmax) (b = -0.156, p = 0.011) and the largest increase in relative wall thickness (RWT) (b = 0.139, p = 0.030), consequently resulting in an LAVmax smaller and an RWT larger at follow-up than other lesion sites (Figure). Lastly, Cx lesions were significantly associated with the largest decrease in ratio between peak early diastolic transmitral flow velocity and peak early diastolic mitral annular tissue velocity (E/e’) (b = -0.262, P &lt;0.001). Cx lesion patients were observed to have elevated E/e’ at baseline, which generally normalised at follow-up (Figure).

Conclusion

The present study suggests that culprit coronary artery lesion site has a differential impact on cardiac remodeling. This information can potentially aid the clinical understanding of cardiac structure and function following ACS according to coronary artery lesion site.

Abstract Figure

Pharmacological inhibition of acetylcholine-regulated potassium current (IK,ACh) and associated A1- and M2-pathways prevent atrial arrhythmogenic changes in a rat model for obstructive sleep apnea

Background

In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase vagal tone and adenosine release, potentially resulting in an increased acetylcholine-regulated potassium current (IK,ACh). Here we elucidated acute atrial electrophysiological effects of obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) and the role of atrial IKACh activation by A1-receptor and M2-receptor activation.

Methods

In sedated spontaneously breathing rats (2% isoflurane), either IK,ACh-inhibitor (XAF-1407: 1mg/kg), M2-receptor inhibitor (atropine; 1μg/kg), A1-receptor inhibitor (Rolofylline; 1μg/kg) or a buffer-based vehicle was perfused (Control). INAP was applied non-invasively by a negative pressure device 14 times throughout 70 minutes. Simulated apneas were maintained for one minute with a four minute resting period. Atrial effective refractory period (AERP) and atrial activation time were acquired by a programmed atrial pacing protocol before, during and after applied INAP throughout the study.

Results

Independent of IK,Ach-inhibition, single INAP applications prolonged transiently atrial activation times (Control: INAP vs. pre-INAP p=0.034; XAF-1407: INAP vs. pre-INAP p=0.039). In control-rats, seventy minutes of repetitive INAP decreased AERP by 15.45±0.06% (vs. baseline p=0.0015), which was reversible upon 1 hour of recovery. AERP shortening correlated with the cumulative pressure applied per body weight (Pearson r=−0.773; p=0.025). Whilst only XAF-1407 and atropine increased baseline AERP, all drug interventions, XAF-1407, atropine and Rolofylline could prevent INAP-associated AERP shortening (end INAP-protocol vs. respective baseline XAF-1407 p=0.994; atropine p=0.984; Rolofylline p=0.951). Drops in oxygen saturation and applied INAP were comparable in all groups.

Conclusion

Short-term simulated OSA is associated with progressive AERP shortening, which was determined by the cumulative negative airway pressure applied. This potentially represents an important insight in future OSA treatment. Pharmacological IK,ACh inhibition prevented INAP-associated AERP-shortening suggesting an involvement in acute atrial arrhythmogenesis in OSA. However, if IK,Ach and its potential upstream activating A1- and M2-pathway pose a pharmacological treatment target for OSA-patients with AF, requires further investigation.

Funding Acknowledgement

Type of funding source: None

Obstructive respiratory events transiently impair electromechanical coupling and increase premature ventricular contraction rate in a drug-induced Long-QT-2 pig model

Background

Obstructive sleep apnea (OSA) is characterized by intermittent negative thoracic pressure fluctuations and intermittent hypoxemic events. Recent findings associate OSA with impaired ventricular repolarization during sleep and increased risk of sudden cardiac death, which may have special implications for Long-QT-2-syndrome patients. Therefore, we elucidated changes in ventricular repolarization and electromechanical coupling (electromechanical window; EMW) during either obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) or hypoxemic events simulated by intermittent hypoxia (IH) in vehicle (VEH) and dofetilide (DOF) treated pigs, as a simulation of drug induced Long-QT-2 syndrome.

Methods

In sedated spontaneously breathing pigs, either VEH or DOF (50 μg/kg) was perfused and INAP was applied by a negative pressure device connected to the intubation tube. For IH-application the device was connected and left turned off. INAP or IH was maintained for 75 seconds followed by a ten-minute resting period. In order to evaluate the electromechanical window, the time difference between electrical (QT-duration) and mechanical systole (Q-wave to the end of left ventricular pressure signal, QLVPend) was measured before (pre-INAP/-IH), during and 60 seconds after INAP/IH (post-INAP/-IH). Incidence rates of premature ventricular contractions (PVC) and ventricular tachycardia were compared pre- to post-INAP/-IH.

Results

In VEH-pigs, EMW shortened throughout INAP and post-INAP periods steadily (VEH: pre-INAP: 81.69±2.31ms; INAP: 55.65±6.13ms; post-INAP: 38±8.89ms. p=0.008). EMW shortening during post-INAP was associated with an increase in PVCs (VEH: pre-INAP 5.41±1.87 vs. post-INAP 26.5±8.15; p=0.04). In DOF-pigs, INAP-associated EMW-shortening was further potentiated (DOF: pre-INAP: 61.16±7.18ms; INAP: 38.09±9.84ms; post-INAP: 14.93±9.24ms. p=0.016), which was associated with an increase in PVCs (DOF: pre-INAP 4.75±2.36 vs. post-INAP 36.58±10.92; p=0.017). Administration of Atenolol could prevent post-INAP shortening of the EMW and decrease counts of premature ventricular contractions. While desaturations were comparable in INAP and IH, IH did not result in EMW-shortening or increased arrhythmia risk.

Conclusion

Transient dissociation of the ventricular electromechanical coupling during a simulated obstructive apnea, but not during IH, creates a dynamic and sympathetically driven arrhythmogenic substrate. Apnea associated ventricular electromechanical uncoupling was aggravated in a drug-induced Long-QT-2 simulation. Whether OSA represents a modifiable arrhythmogenic risk factor in Long-QT-2-patients warrants further studies.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Novo nordisk fonden

Uncarboxylated matrix Gla-protein: A biomarker of vitamin K status and cardiovascular risk

BACKGROUND

Dephosphorylated uncarboxylated matrix Gla-protein (dp-ucMGP) is a biomarker of functional vitamin K status. High plasma dp-ucMGP concentrations reflect a low vitamin K status and have been related to vascular calcification. Our aims were to assess plasma levels of dp-ucMGP and their association with cardiovascular risk in a general population.

METHODS

Plasma dp-ucMGP measurements were performed using the IDS-iSYS InaKtif MGP assay in 491 consecutive participants in a Danish general population study (229 males and 262 females, aged 19-71 years). Multivariable linear and logistic regressions were used to assess the association between dp-ucMGP levels and cardiovascular risk factors.

RESULTS

Mean ± standard deviation (SD) for dp-ucMGP was 465 ± 181 pmol/L, and upper 95th percentile was 690 pmol/L. In logistic regression analyses, an increase in dp-ucMGP category (<300, 300-399, 400-499, ≥500 pmol/L) was positively associated with obesity, odds ratio (OR) 2.27 (95% confidence interval (CI) 1.54-3.33), history of cardiovascular disease, OR 1.77 (CI 1.02-3.05), and above-median estimated pulse wave velocity (ePWV), OR 1.54 (CI 1.21-1.96), when adjusted for age, sex, and lifestyle factors. 1 SD increase in diastolic and systolic blood pressure (BP) corresponded to a 5.5% (CI 2.9-8.0%) and 4.7% (CI 2.1-7.4%) increase in dp-ucMGP, respectively, when adjusted for age and sex.

CONCLUSION

Plasma dp-ucMGP levels were positively associated with obesity, BP, ePWV, and history of cardiovascular disease. These findings support that dp-ucMGP is a biomarker of cardiovascular risk, and that vitamin K status could play a role in vascular calcification. The strong association with obesity deserves further attention.

741Pharmacological inhibition of the acetylcholine-regulated potassium channel (IK,ACh) prevents atrial arrhythmogenic changes in a rat model for obstructive sleep apnea

Background

In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase vagal tone, resulting in an increased acetylcholine-regulated potassium current (IK,ACh). Here we elucidated acute atrial electrophysiological effects of obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) and the role of atrial IKACh activation.

Methods

In sedated spontaneously breathing rats (2% isoflurane), either IK,ACh-inhibitor (XAF-1407: 1mg/kg) or a buffer-based vehicle was perfused (Control). INAP was applied non-invasively by a negative pressure device 14 times throughout 70 minutes. Simulated apneas were maintained for one minute with a four minute resting period. Atrial effective refractory period (AERP), inducible atrial fibrillation (AF)-durations and atrial activation time were acquired by a programmed atrial pacing protocol before, during and after applied INAP throughout the study.

Results

During single INAP applications atrial activation times prolonged transiently in both groups (Control: INAP vs. pre-INAP p = 0.034; XAF-1407: INAP vs. pre-INAP p = 0.039). In control-rats, seventy minutes of repetitive INAP prolonged P-wave duration (+10.8 ± 2.7% vs. baseline, p = 0.008) and decreased AERP by 14.6 ± 3.1% (vs. baseline p = 0.001). AERP shortening correlated with the cumulative pressure applied per body weight (Pearson r= -0.773; p= 0.025). XAF-1407 could prevent P-wave prolongation and AERP shortening. Inducible AF-durations (CTR 0.94 ± 0.34s vs. XAF-1407 0.1 ± 0.09s p = 0.049) were shorter in XAF-1407 treated rats. Drops in oxygen saturation or applied INAP were comparable in control and XAF-1407 rats.

Conclusion

Short-term simulated OSA is associated with AF-related arrhythmogenic changes, which could be prevented by pharmacological IK,ACh inhibition. Moreover, the cumulative negative airway pressure applied determined aERP shortening and may represent a target for OSA treatment. These findings have important implications for the antiarrhythmic management of AF patients with OSA.

1270Early systolic lengthening in patients with ST-segment elevation myocardial infarction: a novel predictor of cardiovascular events

Background

Early systolic lengthening (ESL) may occur in ischemic myocardial segments with reduced contractile force. We sought to evaluate the prognostic potential of ESL in patients with ST-segment elevated myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI).

Methods

We prospectively enrolled 372 patients with STEMI who were treated with primary PCI. All patients underwent a speckle tracking echocardiographic examination with a median of 2 days (interquartile range 1, 3 days) after the PCI. We assessed a novel viability index, the ESL index, defined as: (100 x [peak positive systolic strain/peak negative global strain]), obtained as the average value from all 18 segments. We also calculated ESL duration from 18 segments, defined as time from onset of QRS complex on the electrocardiogram to time to peak of positive systolic strain.

Results

During a median follow-up time of 5.3 years (interquartile range 2.5, 6.0), 145 (39%) experienced major adverse cardiovascular events (MACEs), which was a composite of incident heart failure, new myocardial infarction and all-cause mortality. The ESL index and ESL duration were significantly increased in culprit lesion areas (6.7±6.2% vs. 5.0±4.1% and 43±33ms vs. 33±24ms, P<0.001 for both). In Cox proportional hazards models the ESL index (HR 1.27 per 1% increase, 95% CI 1.13–1.43, P<0.001, Fig A) and ESL duration (HR 1.49 per 1ms increase, 95% CI 1.15–1.92, P=0.002, Fig B) yielded prognostic information on MACE. Both associations remained significant after adjusting for clinical (age, sex, hypertension, heart rate), echocardiographic (LVMI, E/e', WMSI, LVEF, postsystolic index) and invasive (postprocedural TIMI flow, TnI) confounders. Additionally, tertiles of the ESL index and ESL duration yielded significant prognostic information on MACE (Fig C-D).

ESL index and ESL duration and MACE

Conclusions

Assessment of ESL following primary PCI in patients with STEMI yields independent and significant prognostic information on the future risk of cardiovascular events.

3149Regional strain patterns according to hypertension and left ventricular hypertrophy in the general population

Background

A pattern of reduced basal longitudinal strain (BLS) is often observed in hypertension (HT) and with altered left ventricular (LV) geometry. Whether this pattern is associated with poor outcome is unclear. We hypothesized that BLS becomes incrementally more impaired in the transition from HT to LV hypertrophy (LVH) and is a predictor of outcome.

Methods

We investigated 1,096 participants from a community-based cohort study who had an echocardiogram with speckle tracking performed. Regional strain was calculated as: BLS, midventricular and apical strain. The participants were stratified by LV geometry: LVH vs. non-LVH (LVH defined as left ventricular mass index >116 g/m2 for men and >96g/m2 for women). Outcome was major adverse cardiovascular events (MACE) defined as incident myocardial infarction, heart failure, and cardiovascular death.

Results

BLS and midventricular strain were significantly reduced when comparing normal participants without HT to participants with HT, whereas only BLS was reduced when comparing participants with HT to those with LVH (figure). Overall, patients with LVH showed both reduced BLS and midventricular strain (BLS: −17.5 vs −19.2%, p<0.001; midventricular strain: −19.2 vs. −19.9%, p=0.007 for LVH and non-LVH, respectively) compared to non-LVH, whereas apical strain was similar between groups.

During a median follow-up of 12.9 years (13.5; 14.9 years) there were 139 events. Only BLS was reduced in patients with MACE (BLS: −18.0 vs −19.1%, p=0.002) compared to patients without outcome. Both BLS and midventricular strain were univariable predictors of MACE in patients with LVH (BLS: HR=1.20 [1.04; 1.20], p=0.002; midventricular strain: HR=1.08 [1.00; 1.17], p=0.049) but not in patients without LVH (BLS: HR=1.02 [0.97; 1.08], p=0.46; midventricular strain: HR=1.01 [0.94; 1.07], p=0.88). Both measures were independent predictors after multivariable adjustment for clinical risk factors: age, gender, smoking, hypertension, and cholesterol (BLS: HR=1.08 [1.00; 1.16, p=0.048; midventricular strain: HR=1.10 [1.00; 1.20], p=0.049).

Regional strain by HT and LV geometry

Conclusion

BLS and midventricular strain, but not apical strain, becomes incrementally impaired in the transition from normal to LVH, and is associated with poor outcome. In regional strain analyses, BLS provides the highest predictive value for outcome in patients with LVH.

Acknowledgement/Funding

None

P2561Withdrawal of simulated obstructive sleep apnea partially reverses atrial arrhythmogenic substrate in rats

Background

Obstructive sleep apnea (OSA) is associated with structural alterations of the left atria (LA) and increased occurrence of atrial fibrillation (AF). Obstructive respiratory events lead to intermittent hypoxia (IH) and ineffective inspiration against the occluded upper airways, which result in intrathoracic and cardiac transmural pressure changes. Data on reversibility of LA-structural remodeling processes after withdrawal of OSA are still missing.

Objectives

Aim of the study was to develop a novel AF animal model mimicking intrathoracic pressure changes in addition to IH and to analyze the effect of OSA-withdrawal on atrial remodeling reversibility.

Method

In sedated rats (2% isoflurane), IH (n=9) was applied by intermittent increase in the respiratory dead volume. Standardized obstructive respiratory events were induced by defined intermittent negative upper airway pressure (INAP = inverse CPAP) applied via a customized mask connected to a negative pressure device (n=9). One minute of IH or INAP was followed by a rest period of nine minutes for four hours every second day. Rats with comparable anesthesia were used as controls (CTR). After three weeks, the animals were sacrificed. To analyze atrial structural remodeling reversibility, additional INAP-rats (n=5) were sacrificed after INAP-withdrawal of three weeks and compared to respective CTR (n=7).

Result

Blood pressure was not affected by IH or INAP. Intermittent desaturation and post-apneic hyperventilation were comparable in INAP- and IH-rats, but INAP-rats showed significantly higher breathing efforts during apneas compared to IH-rats. LA connexin43 (Cx43) protein expression assessed by quantitative immunofluorescence was reduced in both groups compared to CTR (0.77±0.07% in CTR vs. 0.45±0.06% in IH, p=0.02; CTR vs. 0.39±0.06% in INAP, p=0.005). However, LA interstitial fibrosis content (7.03±0.58% vs. CTR, p=0.01) and LA myocyte diameters (13.23±0.34μm vs. CTR, p=0.03) were increased in INAP-rats, but not in IH-rats. This was associated with longer inducible AF-durations in INAP-rats (11.65±4.43s vs. 0.72±0.33s in CTR, p=0.03) but not in IH-rats (1.28±0.33s vs. CTR, p=0.31). Three weeks of INAP-withdrawal (INAP-W) normalized interstitial fibrosis content (INAP-W vs. CTR, p=0.50) and LA-myocyte diameter (INAP-W vs. CTR, p=0.31). However, LA Cx43 protein expression remained low after three weeks of INAP withdrawal and inducible AF-episodes were still prolonged compared to respective CTR.

Conclusion

Application of INAP in rats mimics important components of OSA beyond IH and allows the study of an arrhythmogenic substrate in the atrium independent of the development of risk factors. In our model, withdrawal of INAP resulted in partial reversibility of structural LA remodeling but was not sufficient to abolish inducible AF-episodes completely. Future clinical studies are warranted to determine the anti-arrhythmic effect of isolated sleep apnea treatment in AF-patients.

Acknowledgement/Funding

Else Kröner-Fresenius-Stiftung, SFB-TRR219-M02/S-02

2138Usefulness of left atrial strain for predicting incident atrial fibrillation and ischemic stroke in the general population

Background

Left atrial (LA) enlargement is an established independent predictor of incident atrial fibrillation (AF). However, the prognostic value of left atrial peak reservoir strain (LA RS) in predicting incident AF in participants from the general population is currently unknown. It is our hypothesis that decreased LA RS can reveal early atrial dysfunction.

Purpose

The aim of this study was to investigate if LA RS can be used to predict AF and ischemic stroke in the general population.

Methods

A total of 405 participants (mean age 56±16 years, 41% male) from the general population underwent a health examination including two-dimensional speckle tracking echocardiography of the LA. LA RS was calculated as the average from the three apical views. The primary endpoint was incident AF at follow-up. All participants with known AF and prior stroke at baseline were excluded (n=54). The secondary endpoint consisted of the composite of AF and ischemic stroke.

Results

During a median follow-up of 16 years (interquartile range, 13.6–16.2 years), 36 participants (9%) were diagnosed with incident AF and 30 (7%) experienced an ischemic stroke, resulting in 66 (16%) experiencing the composite outcome. The risk of AF increased incrementally with decreasing tertile of LA RS, being approximately 10-fold higher in the 1st tertile as compared to the 3rd tertile (HR 9.82; 95% CI (2.95–32.63), p<0.001; figure).

LA RS was a univariable predictor of AF with 41% increased risk per 5% decrease in LA RS (per 5% decrease: HR 1.41; 95% CI (1.18–1.67), p<0.001). However, the prognostic value of LA RS was modified by age (p=0.002 for interaction). After adjusting for clinical and echocardiographic parameters the LA RS predicted AF in participants aged <65 years (per 5% decrease: HR 1.86; 95% CI (1.20–2.90), p=0.006). In contrast, LA RS did not predict AF in participants aged >65 years (per 5% decrease: HR 0.95; 95% CI (0.73–1.23), p=0.69).

LA RS was also a univariable predictor of the composite outcome of AF and ischemic stroke (per 5% decrease: HR 1.29; 95% CI (1.14–1.46), p<0.001). After multivariable adjustment the LA RS predicted AF and ischemic stroke in participants aged <65 years (per 5% decrease: HR 1.33; 95% CI (1.03–1.72), p=0.030).

Furthermore, LA RS provided incremental prognostic information over the left atrial volume index (LAVI) with regard to predicting AF (Harrell's C-statistics 0.69 vs. 0.75, p=0.044) and the composite of AF and ischemic stroke (Harrell's C-statistics 0.59 vs. 0.66, p=0.027) in participants from the general population.

Conclusion

In a low risk general population, the LA RS provides novel prognostic information on the long-term risk of AF and ischemic stroke, especially in participants aged <65 years. In addition, LA RS provides incremental prognostic information over the LAVI in predicting AF and ischemic stroke in the general population.

P6294NLRP3 inflammasome is activated in the atrium of an ovine model of sustained obesity

Introduction

Obesity and enhanced inflammatory response are two independent risk factors involved in the pathogenesis of atrial fibrillation (AF). Components of the NLRP3 inflammasome have been found to be expressed in cardiomyocytes and cardiac fibroblasts and that increased inflammasome activation contributes to the pathogenesis of AF. The NLRP3 inflammasome is a multi-protein signaling complex that is activated in two steps: 1st) a priming event that includes a NFκB-activating stimuli which increases the expression of pro-inflammatory cytokines, and 2nd) a triggering event that includes the assembly of the inflammasome complex and activation of caspase-1 which promotes the production of pro-inflammatory cytokines like interleukin 1 beta (IL-1b).

Purpose

We used a sheep model of sustained obesity to characterize the association between atrial myocardial fat infiltration, atrial activation of the NLRP3 inflammasome and the development of an atrial arrhythmogenic substrate for AF.

Methods

Eight sheep were fed ad libitum calorie-dense diet over 40 weeks to gain weight and were maintained in this state of sustained obesity for another 40 weeks. Eight lean, weight-controlled and aged-matched sheep served as control. Atrial fat infiltration was determined by oil-red staining and NLRP3 inflammasome activation was assessed by immunoblot in atrial whole-tissue lysate. Atrial effective refractory periods (aERPs) were evaluated (twice diastolic threshold, cycle length (CL) of 400 ms, S1S2 -protocol).

Results

Sustained obesity was associated with increased atrial fat infiltration (lean: 0.8±0.3% vs. obese: 2.3±1.2%, p=0.1) and shorter aERP (lean: 169±22ms vs. obese: 138±26ms, p=0.03). Protein levels of caspase-1 and mature IL-1β were significantly enhanced (p=0.04 and p=0.01, respectively). Further shortening of aERP correlated with increasing atrial protein levels of caspase-1 (r=0.59, p=0.02). In contrast, levels of TNFα and NFκB were not significantly changed in atria of sheep with sustained obesity.

Conclusions

Sustained obesity is associated with increased expression of NLRP3 inflammasome-related proteins and the development of an arrhythmogenic substrate for AF. Our study suggest that the increased activity is due to increased triggering, rather than increased gene transcription. Whether NLRP3 inflammasome activation represents a modifiable target to prevent AF in obesity warrants further study.

Light wine consumption is associated with a lower odd for cardiovascular disease in chronic kidney disease

AIMS

To examine the association between wine consumption and the prevalence of chronic kidney disease (CKD) and cardiovascular disease (CVD).

DATA SYNTHESIS

We performed a cross-sectional logistic regression analysis of National Health and Nutrition Examination Survey (NHANES) in participants 21 years of age or older from 2003 to 2006 in a large representative study of the U.S.

POPULATION

Wine consumption was categorized as none (0 glass per day), light (<1 glass per day), or moderate (≥1 glasses per day). Prevalent CKD was defined as a urine albumin/creatinine ratio (UACR) ≥30 mg/g or estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m². CVD was defined as history of CVD including angina, myocardial infarction, or stroke. Only 27 (0.5%) individuals reported moderate wine consumption, whereas 57.5% and 42% reported abstinence and light wine consumption, respectively. Light wine consumption was associated with a lower prevalence of CKD as opposed to abstinence in unadjusted analysis. After adjusting for demographics and CVD risk factors light wine consumption was associated with lower prevalence of CKD defined as UACR ≥30 mg/g but not with low eGFR. Furthermore, light wine consumption was associated with significantly lower rates of CVD in the general population and in subjects with CKD. The adjusted odd of CVD for those with light wine consumption was 0.72 (CI 0.52-0.99, p = 0.046) for the subjects with CKD.

CONCLUSION

These data suggest that light wine consumption (compared to abstinence) is associated with lower prevalence of CKD and a lower odd of CVD in those with CKD in the U.S.

Antiarrhythmic and electrophysiologic effects of flecainide on acutely induced atrial fibrillation in healthy horses

BACKGROUND

Only few pharmacologic compounds have been validated for treatment of atrial fibrillation (AF) in horses. Studies investigating the utility and safety of flecainide to treat AF in horses have produced conflicting results, and the antiarrhythmic mechanisms of flecainide are not fully understood.

OBJECTIVES

To study the potential of flecainide to terminate acutely induced AF of short duration (≥ 15 minutes), to examine flecainide-induced changes in AF duration and AF vulnerability, and to investigate the in vivo effects of flecainide on right atrial effective refractory period, AF cycle length, and ventricular depolarization and repolarization.

ANIMALS

Nine Standardbred horses. Eight received flecainide, 3 were used as time-matched controls, 2 of which also received flecainide.

METHODS

Prospective study. The antiarrhythmic and electrophysiologic effects of flecainide were based on 5 parameters: ability to terminate acute pacing-induced AF (≥ 15 minutes), and drug-induced changes in atrial effective refractory period, AF duration, AF vulnerability, and ventricular depolarization and repolarization times. Parameters were assessed at baseline and after flecainide by programmed electrical stimulation methods.

RESULTS

Flecainide terminated all acutely induced AF episodes (n = 7); (AF duration, 21 ± 5 minutes) and significantly decreased the AF duration, but neither altered atrial effective refractory period nor AF vulnerability significantly. Ventricular repolarization time was prolonged between 8 and 20 minutes after initiation of flecainide infusion, but no ventricular arrhythmias were detected.

CONCLUSIONS AND CLINICAL IMPORTANCE

Flecainide had clear antiarrhythmic properties in terminating acute pacing-induced AF, but showed no protective properties against immediate reinduction of AF. Flecainide caused temporary prolongation in the ventricular repolarization, which may be a proarrhythmic effect.

Effect of the I(to) activator NS5806 on cloned K(V)4 channels depends on the accessory protein KChIP2

BACKGROUND AND PURPOSE

The compound NS5806 increases the transient outward current (I(to)) in canine ventricular cardiomyocytes and slows current decay. In human and canine ventricle, I(to) is thought to be mediated by K(V)4.3 and various ancillary proteins, yet, the exact subunit composition of I(to) channels is still debated. Here we characterize the effect of NS5806 on heterologously expressed putative I(to) channel subunits and other potassium channels.

EXPERIMENTAL APPROACH

Cloned K(V)4 channels were co-expressed with KChIP2, DPP6, DPP10, KCNE2, KCNE3 and K(V)1.4 in Xenopus laevis oocytes or CHO-K1 cells.

KEY RESULTS

NS5806 increased K(V)4.3/KChIP2 peak current amplitudes with an EC(50) of 5.3 +/- 1.5microM and significantly slowed current decay. KCNE2, KCNE3, DPP6 and DPP10 modulated K(V)4.3 currents and the response to NS5806, but current decay was slowed only in complexes containing KChIP2. The effect of NS5806 on K(V)4.2 was similar to that on K(V)4.3, and current decay was only slowed in presence of KChIP2. However, for K(V)4.1, the slowing of current decay by NS5806 was independent of KChIP2. K(V)1.4 was strongly inhibited by 10 microM NS5806 and K(V)1.5 was inhibited to a smaller extent. Effects of NS5806 on kinetics of currents generated by K(V)4.3/KChIP2/DPP6 with K(V)1.4 in oocytes could reproduce those on cardiac I(to) in canine ventricular myocytes. K(V)7.1, K(V)11.1 and K(ir)2 currents were unaffected by NS5806.

CONCLUSION AND IMPLICATIONS

NS5806 modulated K(V)4 channel gating depending on the presence of KChIP2, suggesting that NS5806 can potentially be used to address the molecular composition as well as the physiological role of cardiac I(to).

Dual-function vector for protein expression in both mammalian cells and Xenopus laevis oocytes

Both Xenopus laevis oocytes and mammalian cells are widely used for heterologous expression of several classes of proteins, and membrane proteins especially, such as ion channels or receptors, have been extensively investigated in both cell types. A full characterization of a specific protein will often engage both oocytes and mammalian cells. Efficient expression of a protein in both systems have thus far only been possible by subcloning the cDNA into two different vectors because several different molecular requirements should be fulfilled to obtain a high protein level in both mammalian cells and oocytes. To address this problem, we have constructed a plasmid vector, pXOOM, that can function as a template for expression in both oocytes and mammalian cells. By including all the necessary RNA stability elements for oocyte expression in a standard mammalian expression vector, we have obtained a dual-function vector capable of supporting protein production in both Xenopus oocytes and CHO-K1 cells at an expression level equivalent to the levels obtained with vectors optimized for either oocyte or mammalian expression. Our functional studies have been performed with hERGI, KCNQ4, and Kv1.3 potassium channels.

KCNQ4 channel activation by BMS-204352 and retigabine

Activation of potassium channels generally reduces cellular excitability, making potassium channel openers potential drug candidates for the treatment of diseases related to hyperexcitabilty such as epilepsy, neuropathic pain, and neurodegeneration. Two compounds, BMS-204352 and retigabine, presently in clinical trials for the treatment of stroke and epilepsy, respectively, have been proposed to exert their protective action via an activation of potassium channels. Here we show that KCNQ4 channels, stably expressed in HEK293 cells, were activated by retigabine and BMS-204352 in a reversible and concentration-dependent manner in the concentration range 0.1-10 microM. Both compounds shifted the KCNQ4 channel activation curves towards more negative potentials by about 10 mV. Further, the maximal current obtainable at large positive voltages was also increased concentration-dependently by both compounds. Finally, a pronounced slowing of the deactivation kinetics was induced in particular by BMS-204352. The M-current blocker linopirdine inhibited the baseline current, as well as the BMS-204352-induced activation of the KCNQ4 channels. KCNQ2, KCNQ2/Q3, and KCNQ3/Q4 channels were activated to a similar degree as KCNQ4 channels by 10 microM of BMS-204352 and retigabine, respectively. The compounds are, thus, likely to be general activators of M-like currents.

Pharmacological modulation of SK3 channels

Small-conductance, calcium-activated K+ channels (SK channels) are voltage-insensitive channels that have been identified molecularly within the last few years. As SK channels play a fundamental role in most excitable cells and participate in afterhyperpolarization (AHP) and spike-frequency adaptation, pharmacological modulation of SK channels may be of significant clinical importance. Here we report the functional expression of SK3 in HEK293 and demonstrate a broad pharmacological profile for these channels. Brain slice studies commonly employ 4-aminopyridine (4-AP) to block voltage-dependent K+ channels or a methyl derivative of bicuculline, a blocker of gamma-aminobutyric acid (GABA)-gated Cl- channels, in order to investigate the role of various synapses in specialized neural networks. However, in this study both 4-AP and bicuculline are shown to inhibit SK3 channels (IC50 values of 512 microM and 6 microM, respectively) at concentrations lower than those used for brain slice recordings. Riluzole, a potent neuroprotective drug with anti-ischemic, anticonvulsant and sedative effects currently used in the treatment of amyotrophic lateral sclerosis, activates SK3 channels at concentrations of 3 microM and above. Amitriptyline, a tricyclic antidepressive widely used clinically, inhibits SK3 channels with an IC50 of 39.1 +/- 10 microM (n=6).

An ERG channel inhibitor from the scorpion Buthus eupeus

The isolation of the peptide inhibitor of M-type K(+) current, BeKm-1, from the venom of the Central Asian scorpion Buthus eupeus has been described previously (Fillipov A. K., Kozlov, S. A., Pluzhnikov, K. A., Grishin, E. V., and Brown, D. A. (1996) FEBS Lett. 384, 277-280). Here we report the cloning, expression, and selectivity of BeKm-1. A full-length cDNA of 365 nucleotides encoding the precursor of BeKm-1 was isolated using the rapid amplification of cDNA ends polymerase chain reaction technique from mRNA obtained from scorpion telsons. Sequence analysis of the cDNA revealed that the precursor contains a signal peptide of 21 amino acid residues. The mature toxin consists of 36 amino acid residues. BeKm-1 belongs to the family of scorpion venom potassium channel blockers and represents a new subgroup of these toxins. The recombinant BeKm-1 was produced as a Protein A fusion product in the periplasm of Escherichia coli. After cleavage and high performance liquid chromatography purification, recombinant BeKm-1 displayed the same properties as the native toxin. Three BeKm-1 mutants (R27K, F32K, and R27K/F32K) were generated, purified, and characterized. Recombinant wild-type BeKm-1 and the three mutants partly inhibited the native M-like current in NG108-15 at 100 nm. The effect of the recombinant BeKm-1 on different K(+) channels was also studied. BeKm-1 inhibited hERG1 channels with an IC(50) of 3.3 nm, but had no effect at 100 nm on hEAG, hSK1, rSK2, hIK, hBK, KCNQ1/KCNE1, KCNQ2/KCNQ3, KCNQ4 channels, and minimal effect on rELK1. Thus, BeKm-1 was shown to be a novel specific blocker of hERG1 potassium channels.

Expression of heterologous genes from an IRES translational cassette in replication competent murine leukemia virus vectors

We describe replication competent retroviruses capable of expressing heterologous genes during multiple rounds of infection. An internal ribosome entry site (IRES) from encephalomyocarditis virus was inserted in the U3 region of Akv- and SL3-3-murine leukemia viruses (MLV) to direct translation of neo or the enhanced green fluorescence protein gene (EGFP). Akv-MLV's with IRES-neo and IRES-EGFP cassettes replicated with titers of about 10(6) infectious units/ml while SL3-3-MLV with IRES-neo gave about 10(3)-fold lower titers. Interestingly, RNA analysis showed a drastic reduction in the amount of spliced env mRNA for the SL3-3 derived vector relative to the Akv derived vectors, seemingly contributing to its low replication capacity. The EGFP expressing Akv-MLV was genetically stable for multiple rounds of infection; marker-cassette deletion revertants appeared after several replication rounds and these revertants only slowly became dominant in the virus population.

Evaluation of isofagomine and its derivatives as potent glycosidase inhibitors

A pseudo-aza-monosaccharide and several pseudo-aza-disaccharide compounds were constructed based on replacement of the anomeric carbon with a nitrogen and the ring oxygen with a carbon. The inhibition constants of these compounds toward five different glycosidases, alpha-glucosidase, beta-glucosidase, isomaltase, alpha-mannosidase, and glucoamylase, were obtained. Isofagomine, the pseudo-aza-monosaccharide, shows a broad spectrum of strong inhibition against glycosidases. It is the most potent inhibitor of beta-glucosidase from sweet almonds reported to date and also a strong inhibitor of glucoamylase, isomaltase, and alpha-glucosidase. Isofagomine inhibits beta-glucosidase, glucoamylase, and isomaltase more strongly than 1-deoxynojirimycin where the ring oxygen has been replaced with a nitrogen. The alpha-1,6- linked pseudo-disaccharide showed very strong inhibition toward glucoamylase, being nearly as potent an inhibitor as acarbose. Pseudo-disaccharides in which the anomeric nitrogen was methylated to favor formation of either the alpha or beta substrate linkage generally had weakened inhibition for the glycosidases studied most likely due to steric interference with the various active sites. These results indicate that the presence of a basic group at the anomeric center is important for carbohydrase inhibition. The presence of a charged carboxylate group near the anomeric carbon which interacts with the basic nitrogen is suggested for these enzymes, particularly for beta-glucosidase. The presence of a second alpha-linked glucosyl residue is also critical for strong inhibition of glucoamylase.