Neuropeptide Y increases 4-aminopyridine-sensitive transient outward potassium current in rat ventricular myocytes

Circulating Neuropeptide Y May Be a Biomarker for Diagnosing Atrial Fibrillation

INTRODUCTION

Sympathetic nervous system disorder promotes atrial fibrillation (AF), and neuropeptide Y (NPY) is an important neurotransmitter. This study aimed to explore the predictive value of plasma NPY in patients with AF.

METHODS

Five hundred seventy-six patients were divided into AF (including paroxysmal and long-standing persistent AF; 360) and sinus rhythm (SR) groups (216). NPY level was detected using enzyme-linked immunosorbent assay, and NPY mRNA expression level was detected using quantitative polymerase chain reaction. Logistic regression was used to analyse the risk factors for AF; the correlations between blood NPY level and age, body mass index (BMI), left ventricular ejection fraction, left atrial diameter (LAD), and European Heart rate Association (EHRA) score in patients with AF were determined. The receiver operating characteristic (ROC) curve was utilised to predict AF.

RESULTS

Plasma NPY levels were found to be higher in patients with AF than in patients with SR and in patients with long-standing persistent AF than in patients with paroxysmal AF; blood NPY mRNA levels were higher in the paroxysmal and long-standing persistent AF groups compared to the SR group (p < 0.05). Increased age {odds ratio (OR) = 1.201 (95% confidence interval [CI]: 1.01, 1.427)} and high NPY [OR = 1.239 (95% CI: 1.022, 1.501)] were factors found to affect AF detrimentally. NPY was associated with BMI (r = 0.5856, p < 0.05), LAD (r = 0.4023, p < 0.05), and EHRA score (r = 0.898, p < 0.05). The ROC curve for the predictive value of plasma NPY levels for AF showed an area under the curve (AUC) value of 0.919 (p < 0.05), while that for long-standing persistent AF showed an AUC of 0.784 (p < 0.05).

CONCLUSION

Circulating NPY may be a promising molecular biomarker of AF.

The cardiac sympathetic co-transmitter neuropeptide Y is pro-arrhythmic following ST-elevation myocardial infarction despite beta-blockade

AIMS

ST-elevation myocardial infarction is associated with high levels of cardiac sympathetic drive and release of the co-transmitter neuropeptide Y (NPY). We hypothesized that despite beta-blockade, NPY promotes arrhythmogenesis via ventricular myocyte receptors.

METHODS AND RESULTS

In 78 patients treated with primary percutaneous coronary intervention, sustained ventricular tachycardia (VT) or fibrillation (VF) occurred in 6 (7.7%) within 48 h. These patients had significantly (P < 0.05) higher venous NPY levels despite the absence of classical risk factors including late presentation, larger infarct size, and beta-blocker usage. Receiver operating curve identified an NPY threshold of 27.3 pg/mL with a sensitivity of 0.83 and a specificity of 0.71. RT-qPCR demonstrated the presence of NPY mRNA in both human and rat stellate ganglia. In the isolated Langendorff perfused rat heart, prolonged (10 Hz, 2 min) stimulation of the stellate ganglia caused significant NPY release. Despite maximal beta-blockade with metoprolol (10 μmol/L), optical mapping of ventricular voltage and calcium (using RH237 and Rhod2) demonstrated an increase in magnitude and shortening in duration of the calcium transient and a significant lowering of ventricular fibrillation threshold. These effects were prevented by the Y1 receptor antagonist BIBO3304 (1 μmol/L). Neuropeptide Y (250 nmol/L) significantly increased the incidence of VT/VF (60% vs. 10%) during experimental ST-elevation ischaemia and reperfusion compared to control, and this could also be prevented by BIBO3304.

CONCLUSIONS

The co-transmitter NPY is released during sympathetic stimulation and acts as a novel arrhythmic trigger. Drugs inhibiting the Y1 receptor work synergistically with beta-blockade as a new anti-arrhythmic therapy.

The Role of Neuropeptide Y in Cardiovascular Health and Disease

Neuropeptide Y (NPY) is an abundant sympathetic co-transmitter, widely found in the central and peripheral nervous systems and with diverse roles in multiple physiological processes. In the cardiovascular system it is found in neurons supplying the vasculature, cardiomyocytes and endocardium, and is involved in physiological processes including vasoconstriction, cardiac remodeling, and angiogenesis. It is increasingly also implicated in cardiovascular disease pathogenesis, including hypertension, atherosclerosis, ischemia/infarction, arrhythmia, and heart failure. This review will focus on the physiological and pathogenic role of NPY in the cardiovascular system. After summarizing the NPY receptors which predominantly mediate cardiovascular actions, along with their signaling pathways, individual disease processes will be considered. A thorough understanding of these roles may allow therapeutic targeting of NPY and its receptors.

Autonomic control of the heart: going beyond the classical neurotransmitters

Acute myocardial infarction and congestive cardiac failure are characterized by high levels of cardiac sympathetic drive. In these conditions, sympathetic neurotransmitters such as neuropeptide Y (NPY) can be released in addition to noradrenaline, and plasma levels correlate with infarct size and mortality. Even in the presence of β-blockers, NPY is able to bind to its own receptors located on cholinergic ganglia and ventricular myocytes. In this symposium report, I review the evidence that NPY can inhibit acetylcholine release during vagus nerve stimulation and limit the subsequent bradycardia. I also present preliminary, as yet unpublished data, demonstrating that NPY may be pro-arrhythmic by directly influencing ventricular electrophysiology. Targeting NPY receptors pharmacologically may therefore be a useful therapeutic strategy both to reduce heart rate and to prevent arrhythmias in the setting of myocardial infarction and chronic heart failure. Such medications would be expected to act synergistically with β-blockers, angiotensin-converting enzyme inhibitors and implantable cardiac devices, such as defibrillators and vagus nerve stimulators.

The cardiac sympathetic co-transmitter galanin reduces acetylcholine release and vagal bradycardia: implications for neural control of cardiac excitability

The autonomic phenotype of congestive cardiac failure is characterised by high sympathetic drive and impaired vagal tone, which are independent predictors of mortality. We hypothesize that impaired bradycardia to peripheral vagal stimulation following high-level sympathetic drive is due to sympatho-vagal crosstalk by the adrenergic co-transmitters galanin and neuropeptide-Y (NPY). Moreover we hypothesize that galanin acts similarly to NPY by reducing vagal acetylcholine release via a receptor mediated, protein kinase-dependent pathway. Prolonged right stellate ganglion stimulation (10 Hz, 2 min, in the presence of 10 μM metoprolol) in an isolated guinea pig atrial preparation with dual autonomic innervation leads to a significant (p < 0.05) reduction in the magnitude of vagal bradycardia (5 Hz) maintained over the subsequent 20 min (n = 6). Immunohistochemistry demonstrated the presence of galanin in a small number of tyrosine hydroxylase positive neurons from freshly dissected stellate ganglion tissue sections. Following 3 days of tissue culture however, most stellate neurons expressed galanin. Stellate stimulation caused the release of low levels of galanin and significantly higher levels of NPY into the surrounding perfusate (n = 6, using ELISA). The reduction in vagal bradycardia post sympathetic stimulation was partially reversed by the galanin receptor antagonist M40 after 10 min (1 μM, n = 5), and completely reversed with the NPY Y₂ receptor antagonist BIIE 0246 at all time points (1 μM, n = 6). Exogenous galanin (n = 6, 50–500 nM) also reduced the heart rate response to vagal stimulation but had no effect on the response to carbamylcholine that produced similar degrees of bradycardia (n = 6). Galanin (500 nM) also significantly attenuated the release of ³H-acetylcholine from isolated atria during field stimulation (5 Hz, n = 5). The effect of galanin on vagal bradycardia could be abolished by the galanin receptor antagonist M40 (n = 5). Importantly the GalR₁ receptor was immunofluorescently co-localised with choline acetyl-transferase containing neurons at the sinoatrial node. The protein kinase C inhibitor calphostin (100 nM, n = 6) abolished the effect of galanin on vagal bradycardia whilst the protein kinase A inhibitor H89 (500 nM, n = 6) had no effect. These results demonstrate that prolonged sympathetic activation releases the slowly diffusing adrenergic co-transmitter galanin in addition to NPY, and that this contributes to the attenuation in vagal bradycardia via a reduction in acetylcholine release. This effect is mediated by GalR₁ receptors on vagal neurons coupled to protein kinase C dependent signalling pathways. The role of galanin may become more important following an acute injury response where galanin expression is increased.

Neuromodulators of peripheral cardiac sympatho-vagal balance

The traditional model of efferent cardiac noradrenaline and acetylcholine release being driven solely via brainstem integration of circulatory reflex afferent input needs to be modified in the light of the discovery of numerous local cardiac factors that impact on peripheral neuronal neurotransmitter release. These neuromodulators can be intrinsic to sympathetic ganglia or vagal neurons (such as neuronal nitric oxide synthase), act as cotransmitters between these neuronal populations (such as neuropeptide Y) or are released from the myocardium itself to act on neurons in a paracrine manner (such as natriuretic peptides). Both myocardial infarction and congestive heart failure are characterized by enhanced regulation of these neuromodulators. This review will focus on recent evidence that nitric oxide, natriuretic peptides and neuropeptide Y act by converging on neuronal cyclic nucleotide-dependent pathways to alter the autonomic phenotype in both health and disease.

Neuropeptide Y reduces acetylcholine release and vagal bradycardia via a Y2 receptor-mediated, protein kinase C-dependent pathway

The co-transmitter neuropeptide Y (NPY), released during prolonged cardiac sympathetic nerve stimulation, can attenuate vagal-induced bradycardia. We tested the hypothesis that NPY reduces acetylcholine release, at similar concentrations to which it attenuates vagal bradycardia, via pre-synaptic Y2 receptors modulating a pathway that is dependent on protein kinase A (PKA) or protein kinase C (PKC). The Y2 receptor was immunofluorescently colocalized with choline acetyl-transferase containing neurons at the guinea pig sinoatrial node. The effect of NPY in the presence of various enzyme inhibitors was then tested on the heart rate response to vagal nerve stimulation in isolated guinea pig sinoatrial node/right vagal nerve preparations and also on (3)H-acetylcholine release from right atria during field stimulation. NPY reduced the heart rate response to vagal stimulation at 1, 3 and 5 Hz (significant at 100 nM and reaching a plateau at 250 nM NPY, p<0.05, n=6) but not to the stable analogue of acetylcholine, carbamylcholine (30, 60 or 90 nM, n=6) which produced similar degrees of bradycardia. The reduced vagal response was abolished by the Y2 receptor antagonist BIIE 0246 (1 microM, n=4). NPY also significantly attenuated the release of (3)H-acetylcholine during field stimulation (250 nM, n=6). The effect of NPY (250 nM) on vagal bradycardia was abolished by the PKC inhibitors calphostin C (0.1 microM, n=5) and chelerythrine chloride (25 microM, n=6) but not the PKA inhibitor H89 (0.5 microM, n=6). Conversely, the PKC activator Phorbol-12-myristate-13-acetate (0.5 microM, n=7) mimicked the effect of NPY and significantly reduced (3)H-acetylcholine release during field stimulation. These results show that NPY attenuates vagal bradycardia via a pre-synaptic decrease in acetylcholine release that appears to be mediated by a Y2 receptor pathway involving modulation of PKC.

TNF-alpha downregulates transient outward potassium current in rat ventricular myocytes through iNOS overexpression and oxidant species generation

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that has been implicated in the pathogenesis of heart failure. Prolongation of the action potential duration and downregulation of several K(+) currents might participate in the genesis of arrhythmias associated with chronic heart failure. Little information is available related to the mechanism by which TNF-alpha modulates cardiac K(+) channels. The present study analyzes the effect of TNF-alpha on the transient outward K(+) current (I(to)) in rat ventricular myocytes, using the whole cell patch-clamp technique. We found that TNF-alpha is able to induce a significant reduction of I(to) density, modifies its inactivation, and downregulates the Kv4.2 protein expression, while calcium current density is not affected. We have also demonstrated that the reduction of I(to) density induced by TNF-alpha was prevented by the selective inducible nitric oxide synthase (iNOS) inhibitor 1400-W, the protein synthesis inhibitor cycloheximide, the antioxidant tocopherol, and the superoxide dismutase mimetic manganese(III) tetrakis (4-benzoic acid) porphyrin. In addition, a reduced I(to) density was recorded in ventricular myocytes exposed to peroxynitrite, supporting a possible participation of this oxidant in the effects of TNF-alpha on I(to). We conclude that TNF-alpha exposure, through iNOS induction and generation of oxidant species, promotes electrophysiological changes (decreased I(to) and action potential duration prolongation) in rat ventricular myocytes, providing new insights into how cytokines modulate K(+) channels in the heart.

I K1 and I f in ventricular myocytes isolated from control and hypertrophied rat hearts

Electrophysiological properties of inward rectifier potassium current (I (K1)) and hyperpolarization-activated inward current (I (f)) and the protein expression of the Kir2.1 subfamily and the hyperpolarization-activated cation channel 2 (HCN2) and HCN4 were studied in control and hypertrophied myocytes. Electrophysiological experiments were conducted by whole-cell patch-clamp technique, and protein levels of Kir2.1 subfamily and HCN2 and HCN4 isoforms were analysed by Western blot technique. The density of I (f) as well as the protein expression levels of the HCN2 isoform was found to be significantly higher in hypertrophied myocytes, whereas the protein expression level of HCN4 was not detected in any group. I (K1) density and Kir 2.1 protein expression were similar in control and hypertrophied myocytes, but the time-course of the currents was slower in hypertrophied myocytes. Analysis of I (f) and I (K1) in the same control and hypertrophied myocyte at -80 mV showed that cells in which I (f) was present had values of I (K1) density similar to those cells in which I (f) was not observed. In conclusion, although left ventricular hypertrophy involves an up-regulation of I (f) and its molecular correlate HCN2 in the rat ventricle, its contribution to diastolic depolarization would be limited by the low values of I (f) density at potentials close to the resting potential of the ventricular cells.

Neuropeptide Y Is an Essential In Vivo Developmental Regulator of Cardiac I Ca,L

Cell culture studies demonstrate an increase in cardiac L-type Ca 2+ current ( I Ca,L ) density on sympathetic innervation in vitro and suggest the effect depends on neurally released neuropeptide Y (NPY). To determine if a similar mechanism contributes to the postnatal increase in I Ca,L in vivo, we prepared isolated ventricular myocytes from neonatal and adult mice with targeted deletion of the NPY gene ( Npy −/− ) and matched controls ( Npy +/+ ). Whole-cell voltage clamp demonstrates I Ca,L density increases postnatally in Npy +/+ (by 56%), but is unchanged in Npy −/− . Both I Ca,L density and action potential duration are significantly greater in adult Npy +/+ than Npy −/− myocytes, whereas I Ca,L density is equivalent in neonatal Npy +/+ and Npy −/− myocytes. These data indicate NPY does not influence I Ca,L prenatally, but the postnatal increase in I Ca,L density is entirely NPY-dependent. In contrast, there is a similar postnatal negative voltage shift in the I -V relation in Npy +/+ and Npy −/− , indicating NPY does not influence the developmental change in I Ca,L voltage-dependence. Immunoblot analyses and measurements of maximally activated I Ca,L (in presence of forskolin or BayK 8644) show that the differences in current density between Npy +/+ and Npy −/− cannot be attributed to altered Ca 2+ channel α 1C subunit protein expression. Rather, these results suggest that the in vivo NPY-dependent postnatal increase in I Ca,L density in cardiac myocytes results from regulation I Ca,L properties by NPY.