New therapeutic targets in cardiology: heart failure and arrhythmia: HCN channels

Evaluating the applicability of ivabradine in acute heart failure

BACKGROUND

While ivabradine has demonstrated benefits in heart rate control and prognosis for chronic heart failure patients, its application in acute decompensated heart failure remains underexplored.

HYPOTHESIS

For patients with acute decompensated heart failure with reduced ejection fraction (HFrEF) who are intolerant to β-blockers or unable to further titrate their dosage, the use of ivabradine is hypothesized to be effective and safe is improving outcomes.

METHODS

This retrospective, multicenter database analysis included patients with hospitalized decompensated heart failure with a left ventricular ejection fraction of ≤40% from June 1, 2015 to December 31, 2020. The exclusion criteria were a baseline heart rate of <70 bpm, previous use of ivabradine, mortality during admission, existing atrial fibrillation, or atrial flutter. The primary outcome was the composite of cardiovascular death and hospitalization for heart failure.

RESULTS

Of the 4163 HFrEF patients analyzed, 684 (16.4%) were administered ivabradine during their index admission. After matching, there were 617 patients in either group. The results indicated that ivabradine use was not significantly associated with the risk of the primary composite outcome (hazard ratio: 1.10; 95% confidence interval: 0.94-1.29). Similarly, the risk of secondary outcomes and adverse renal events did not significantly differ between the ivabradine and non-ivabradine cohorts (all p > .05).

CONCLUSION

For hospitalized acute decompensated heart failure patients who are intolerant to β-blockers or cannot further titrate them, ivabradine offers a consistent therapeutic effect. No significant disparities were noted between the ivabradine and non-ivabradine groups in heart failure hospitalization and cardiovascular death.

Multitargeting in cardioprotection: An example of biaromatic compounds

A multitarget drug design approach is actively developing in modern medicinal chemistry and pharmacology, especially with regard to multifactorial diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. A detailed study of many well-known drugs developed within the single-target approach also often reveals additional mechanisms of their real pharmacological action. One of the multitarget drug design approaches can be the identification of the basic pharmacophore models corresponding to a wide range of the required target ligands. Among such models in the group of cardioprotectors is the linked biaromatic system. This review develops the concept of a "basic pharmacophore" using the biaromatic pharmacophore of cardioprotectors as an example. It presents an analysis of possible biological targets for compounds corresponding to the biaromatic pharmacophore and an analysis of the spectrum of biological targets for the five most known and most studied cardioprotective drugs corresponding to this model, and their involvement in the biological effects of these drugs.

Shensong Yangxin Capsule Reduces the Susceptibility of Arrhythmia in db/db Mice via Inhibiting the Inflammatory Response Induced by Endothelium Dysfunction

Purpose

The aim of our study was to investigate the mechanism by which the Chinese compound Shensong Yangxin Capsule (SSYX) reduces susceptibility to arrhythmia in db/db mice.

Methods

The db/db mice without drug treatment served as the model group. Other-treated db/db mice were administered SSYX for 8 weeks. Electrocardiogram (ECG), electrical mapping, pathological changes, immunofluorescence staining, real-time quantitative PCR, and Western blot analyses were then conducted.

Results

SSYX decreased arrhythmia susceptibility and shortened the abnormal ECG parameters of db/db mice. Meanwhile, SSYX restored irregular conduction direction and shortened the conduction time of the isolated heart. HE and Masson staining showed that SSYX alleviated inflammatory infiltration and collagen fiber deposition. Western blot showed that SSYX decreased the protein expression of ICAM-1, VCAM-1, and MCP-1 and increased the protein expression of occludin, ZO-1, eNOS, and Cx43. SSYX also increased the content of NO, decreased ET-1, TNF-α, IL-1β, IL-6, MCP-1, and CCR-2 mRNA expression, and increased Kv 4.2, Kv 4.3, Cav 1.2, and Nav 1.5 mRNA expression. Furthermore, SSYX decreased the fluorescence intensity of F4/80 and iNOS, increased the fluorescence intensity of CD31 and eNOS, and improved the Cx43 and α-actinin connection structure in cardiac tissues. The above therapeutic effects of SSYX were inhibited by L-NAME.

Conclusion

SSYX reduced the susceptibility of db/db mice to arrhythmia by inhibiting the inflammatory response and macrophage polarization, and this effect of SSYX occurred through protection of endothelial cell function.

Early administration of ivabradine in patients admitted for acute decompensated heart failure

BACKGROUND

Heart rate (HR) control is important in heart failure (HF) patients with reduced ejection fraction, and ivabradine is indicated for patients with chronic HF and sinus rhythm. However, ivabradine is limited in initiation of ivabradine at acute stage of HF.

MATERIALS AND METHODS

This multi-institutional retrospective study enrolled 30,639 patients who were admitted for HF from January 01, 2013 to December 31, 2018 at Chang Gung Memorial Hospitals. After applying selection criteria, the eligible patients were divided into ivabradine and non-ivabradine groups according to the initiation of ivabradine at the index hospitalization. HR, clinical outcomes including HF hospitalization, all-cause hospitalization, mortality, the composite of cardiovascular (CV) death or HF hospitalization and newly developed atrial fibrillation, and left ventricular ejection fraction (LVEF) and left atrium size were compared between the ivabradine and non-ivabradine groups after inverse probability of treatment weighting (IPTW) analysis after 12 months.

RESULTS

The HR at admission in the ivabradine group (n = 433) was 99.04 ± 20.69/min, compared to 86.99 ± 20.34/min in the non-ivabradine group (n = 9,601). After IPTW, HR was lower in the ivabradine group than that in the non-ivabradine group after 12 months (74.14 ± 8.53 vs. 81.23 ± 16.79 bpm, p = 0.079). However, there were no significant differences in HF hospitalization (HR = 1.02; 95% CI, 0.38-2.79), all-cause hospitalization (HR = 0.95; 95% CI, 0.54-1.68), mortality (HR = 0.87; 95% CI, 0.69-1.08), the composite of CV death or HF hospitalization (HR = 0.87; 95% CI, 0.69-1.08) and newly developed AF between the two groups. In addition, LVEF increased with time in both groups, but there were no significant differences during the observation period.

CONCLUSION

Ivabradine was beneficial in controlling HR when initiated in patients with acute stage of HF, but it did not seem to provide any benefits in reducing HF hospitalization, all-cause hospitalization, and mortality in 1 year after discharge.

Effects of Antiarrhythmic Drugs on Antiepileptic Drug Action-A Critical Review of Experimental Findings

Severe cardiac arrhythmias developing in the course of seizures increase the risk of SUDEP (sudden unexpected death in epilepsy). Hence, epilepsy patients with pre-existing arrhythmias should receive appropriate pharmacotherapy. Concomitant treatment with antiarrhythmic and antiseizure medications creates, however, the possibility of drug–drug interactions. This is due, among other reasons, to a similar mechanism of action. Both groups of drugs inhibit the conduction of electrical impulses in excitable tissues. The aim of this review was the analysis of such interactions in animal seizure models, including the maximal electroshock (MES) test in mice, a widely accepted screening test for antiepileptic drugs.

Linked biaromatic compounds as cardioprotective agents

Cardiovascular diseases (CVDs) are widespread in the modern world, and their number is constantly growing. For a long time, CVDs have been the leading cause of morbidity and mortality worldwide. Drugs for the treatment of CVD have been developed almost since the beginning of the 20th century, and a large number of effective cardioprotective agents of various classes have been created. Nevertheless, the need for the design and development of new safe drugs for the treatment of CVD remains. Literature data indicate that a huge number of cardioprotective agents of various generations and mechanisms correspond to a single generalized pharmacophore model containing two aromatic nuclei linked by a linear linker. In this regard, we put forward a concept for the design of a new generation of cardioprotective agents with a multitarget mechanism of action within the indicated pharmacophore model. This review is devoted to a generalization of the currently known compounds with cardioprotective properties and corresponding to the pharmacophore model of biaromatic compounds linked by a linear linker. Particular attention is paid to the history of the creation of these drugs, approaches to their design, and analysis of the structure-action relationship within each class.

Beneficial Effects of Ivabradine on Post-Resuscitation Myocardial Dysfunction in a Porcine Model of Cardiac Arrest

Background:

Ivabradine selectively inhibits the If current, reducing the heart rate and protecting against myocardial ischemia/reperfusion injury. We investigated the effects of ivabradine on post-resuscitation myocardial function in a porcine model of cardiopulmonary resuscitation.

Methods and Results:

Ventricular fibrillation was induced and untreated for 8 min while defibrillation was attempted after 6 min of cardiopulmonary resuscitation in anesthetized domestic swine. Then the animals were randomized into ivabradine and placebo groups (n = 5 each). Ivabradine and saline were administered at the same volume 5 min after Return of Spontaneous Circulation, followed by continuous intravenous infusion at 0.5 mg/kg for 480 min. Hemodynamic parameters were continuously recorded. Myocardial function was assessed by echocardiography at baseline and at 60, 120, 240, 480 min and 24 h after resuscitation. The serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) and cardiac troponin I (cTnI) were measured by commercial enzyme-linked immunosorbent assay kits. Animals were killed 24 h after resuscitation, and all myocardial tissue was removed for histopathological analysis. The heart rate was significantly reduced from 1 h after resuscitation in the ivabradine group (all P < 0.05). The post-resuscitation mitral E/A and E/e′ velocity ratios and left ventricular ejection fraction were significantly better in the ivabradine than placebo group (P < 0.05). The serum levels of myocardial injury biomarkers (NT-proBNP, cTnI) and the myocardial biopsy scores were significantly lower in the ivabradine than placebo group (P < 0.05). Neurological deficit scores were lower in the IVA group at PR 24 h (P < 0.05).

Conclusions:

Ivabradine improved post-resuscitation myocardial dysfunction, myocardial injury, and post-resuscitation cerebral function, and also slowed the heart rate in this porcine model.

Interactions of antiepileptic drugs with drugs approved for the treatment of indications other than epilepsy

Introduction: Comorbidities of epilepsy may significantly interfere with its treatment as diseases in the general population are also encountered in epilepsy patients and some of them even more frequently (for instance, depression, anxiety, or heart disease). Obviously, some drugs approved for other than epilepsy indications can modify the anticonvulsant activity of antiepileptics. Areas covered: This review highlights the drug-drug interactions between antiepileptics and aminophylline, some antidepressant, antiarrhythmic (class I-IV), selected antihypertensive drugs and non-barbiturate injectable anesthetics (ketamine, propofol, etomidate, and alphaxalone). The data were reviewed mainly from experimental models of seizures. Whenever possible, clinical data were provided. PUBMED data base was the main search source.Expert opinion: Aminophylline generally reduced the protective activity of antiepileptics, which, to a certain degree, was consistent with scarce clinical data on methylxanthine derivatives and worse seizure control. The only antiarrhythmic with this profile of action was mexiletine when co-administered with VPA. Among antidepressants and non-barbiturate injectable anesthetics, trazodone, mianserin and etomidate or alphaxalone, respectively, negatively affected the anticonvulsant action of some antiepileptic drugs. Clinical data indicate that only amoxapine, bupropion, clomipramine and maprotiline should be used with caution. Possibly, drugs reducing the anticonvulsant potential of antiepileptics should be avoided in epilepsy patients.

The rationale for repurposing funny current inhibition for management of ventricular arrhythmia

Management of ventricular arrhythmia in structural heart disease is complicated by the toxicity of the limited antiarrhythmic options available. In others, proarrhythmia and deleterious hemodynamic and noncardiac effects prevent practical use. This necessitates new thinking in therapeutic agents for ventricular arrhythmia in structural heart disease. Ivabradine, a funny current (I_f) inhibitor, has proven safety in heart failure, angina, and inappropriate sinus tachycardia. Although it is commonly known that funny channels are primarily expressed in the sinoatrial node, atrioventricular node, and conducting system of the ventricle, ivabradine is known to exert effects on metabolism, ion homeostasis, and membrane electrophysiology of remodeled ventricular myocardium. This review considers novel concepts and evidence from clinical and experimental studies regarding this paradigm, with a potential role of ivabradine in ventricular arrhythmia.

Heart Rate Control during Experimental Sepsis in Mice: Comparison of Ivabradine and β-Blockers

BACKGROUND

Tachycardia is a hallmark of sepsis. An elevated heart rate could impair ventricular filling and increase myocardial oxygen demand. β-Blockers and ivabradine (a selective inhibitor of If channels in the sinoatrial node) are both able to control sinus tachycardia, with the latter drug being devoid of negative inotropic effect. This work aimed at assessing the hemodynamic effects of ivabradine as compared with a β-blocker (atenolol) during murine peritonitis.

METHODS

Ivabradine (3 μg/g), atenolol (3 μg/g), or placebo was administered intraperitoneally 2 h after induction of peritonitis (cecal ligation and puncture) in male C57BL6 mice. The authors used invasive (left ventricular catheterization) and noninvasive (transthoracic echocardiography) monitoring to assess hemodynamics 20 h after surgery, including heart rate, blood pressure, left ventricular systolic, and diastolic function (n = 10 mice/group). The authors also assessed overall mortality 30 and 60 h after surgery in a distinct subset of animals (n = 20 mice/group). Descriptive data are presented as median (25th to 75th percentile).

RESULTS

As compared with placebo (601 beats/min [547 to 612]), ivabradine (447 beats/min [430 to 496]) and atenolol (482 beats/min [412 to 505]) blunted sepsis-induced tachycardia assessed by transthoracic echocardiography in awake animals (P < 0.001 and P = 0.004, respectively). Unlike ivabradine, atenolol reduced cardiac output, systolic blood pressure, and left ventricular systolic function (as assessed by ejection fraction, maximal left ventricular pressure rise, and anterior wall strain rate) as compared with septic mice receiving placebo. There was no difference in survival 60 h after sepsis induction with ivabradine (6 of 20, 30%) or atenolol (7 of 20, 35%), as compared with placebo (5 of 20, 25%; P = 0.224).

CONCLUSIONS

Heart rate control could be similarly achieved by ivabradine or atenolol, with preservation of blood pressure, cardiac output, and left ventricular systolic function with the former drug.

Beneficial effects of ivabradine in patients with heart failure, low ejection fraction, and heart rate above 77 b.p.m

Aims

Ivabradine has been approved in heart failure with reduced ejection fraction (HFrEF) and elevated heart rate despite guideline‐directed medical therapy (GDMT) to reduce cardiovascular (CV) death and hospitalization for worsening HF. The median value of 77 b.p.m. is the lower bound selected for the regulatory approval in Canada, South Africa, and Australia. Patient‐reported outcomes (PROs) including symptoms, quality of life, and global assessment are considered of major interest in the global plan of care of patients with HF. However, the specific impact of GDMT, and specifically ivabradine, on PRO remains poorly studied. In the subgroup of patients from the Systolic Heart failure treatment with the If inhibitor ivabradine Trial (SHIFT) who had heart rate above the median of 77 b.p.m. (pre‐specified analysis) and for whom the potential for improvement was expected to be larger, we aimed (i) to evaluate the effects of ivabradine on PRO (symptoms, quality of life, and global assessment); (ii) to consolidate the effects of ivabradine on the primary composite endpoint of CV death and hospitalization for HF; and (iii) to reassess the effects of ivabradine on left ventricular (LV) remodelling.

Methods and results

Comparisons were made according to therapy, and proportional hazards models (adjusted for baseline beta‐blocker therapy) were used to estimate the association between ivabradine and various outcomes. In SHIFT, n = 3357 (51.6%) patients had a baseline heart rate > 77 b.p.m. After a median follow‐up of 22.9 months (inter‐quartile range 18–28 months), ivabradine on top of GDMT improved symptoms (28% vs. 23% improvement in New York Heart Association functional class, P = 0.0003), quality of life (5.3 vs. 2.2 improvement in Kansas City Cardiomyopathy Questionnaire overall summary score, P = 0.005), and global assessment [from both patient (improved in 72.3%) and physician (improved in 61.0%) perspectives] significantly more than did placebo (both P < 0.0001). Ivabradine induced a 25% reduction in the combined endpoint of CV death and hospitalization for HF (hazard ratio 0.75; P < 0.0001), which translates into a number of patients needed to be treated for 1 year of 17. Patients under ivabradine treatment demonstrated a significant reduction in LV dimensions when reassessed at 8 months (P < 0.05).

Conclusions

In patients with chronic HFrEF, sinus rhythm, and a heart rate > 77 b.p.m. while on GDMT, the present analysis brings novel insights into the role of ivabradine in improving the management of HFrEF, particularly with regard to PRO (ISRCTN70429960).

Pharmacology of Ivabradine and the Effect on Chronic Heart Failure

Chronic Heart Failure (CHF) is a complex clinical syndrome with a high incidence worldwide. Although various types of pharmacological and device therapies are available for CHF, the prognosis is not ideal, for which, the control of increased Heart Rate (HR) is critical. Recently, a bradycardic agent, ivabradine, is found to reduce HR by inhibiting the funny current (If). The underlying mechanism states that ivabradine can enter the Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels and bind to the intracellular side, subsequently inhibiting the If. This phenomenon can prolong the slow spontaneous phase in the diastolic depolarization, and thus, reduce HR. The clinical trials demonstrated the significant effects of the drug on reducing HR and improving the symptoms of CHF with fewer adverse effects. This review primarily introduces the chemical features and pharmacological characteristics of ivabradine and the mechanism of treating CHF. Also, some expected therapeutic effects on different diseases were also concluded. However, ivabradine, as a typical If channel inhibitor, necessitates additional research to verify its pharmacological functions.

Gene and Protein Expression Profile of Selected Molecular Targets Mediating Electrophysiological Function in Pgc-1α Deficient Murine Atria

Increases in the prevalence of obesity, insulin resistance, and metabolic syndrome has led to the increase of atrial fibrillation (AF) cases in the developed world. These AF risk factors are associated with mitochondrial dysfunction, previously modelled using peroxisome proliferator activated receptor-γ (PPARγ) coactivator-1 (Pgc-1)-deficient murine cardiac models. We explored gene and protein expression profiles of selected molecular targets related to electrophysiological function in murine Pgc-1α^−/− atria. qPCR analysis surveyed genes related to Na⁺-K⁺-ATPase, K⁺ conductance, hyperpolarisation-activated cyclic nucleotide-gated (Hcn), Na⁺ channels, Ca²⁺ channels, and indicators for adrenergic and cholinergic receptor modulation. Western blot analysis for molecular targets specific to conduction velocity (Na_v1.5 channel and gap junctions) was performed. Transcription profiles revealed downregulation of molecules related to Na⁺-K⁺-ATPase transport, Hcn-dependent pacemaker function, Na⁺ channel-dependent action potential activation and propagation, Ca²⁺ current generation, calsequestrin-2 dependent Ca²⁺ homeostasis, and adrenergic α_1D dependent protection from hypertrophic change. Na_v1.5 channel protein expression but not gap junction expression was reduced in Pgc-1α^−/− atria compared to WT. Na_v1.5 reduction reflects corresponding reduction in its gene expression profile. These changes, as well as the underlying Pgc-1α^−/− alteration, suggest potential pharmacological targets directed towards either upstream PGC-1 signalling mechanisms or downstream ion channel changes.

Prognosis of heart failure treated with digoxin or with ivabradine: A cohort study in the community

BACKGROUND

Resting heart rate (HR) reduction with ivabradine (IVA) improves outcomes of patients with heart failure and reduced ejection fraction (HFrEF). Nevertheless, the best option to slow HR in patients with HFrEF treated with beta-blockers and a HR >70 bpm is unsettled.

AIMS

To evaluate whether, in patients with HFrEF, commencing therapy with digoxin (CT-DIG) is associated to a worse prognosis than commencing treatment with ivabradine (CT-IVA).

METHODS

Observational study over 10 years on 2364 patients with HFrEF in sinus rhythm and a HR >70 bpm. Main outcomes were mortality, hospitalisations and visits. We analyse the independent relationship of CT-DIG or CT-IVA with the prognosis, stratifying patients for cardiovascular comorbidity, and for other potential confounders (378 patients who CT-DIG vs another 355 patients who CT-IVA vs another 1631 patients non-exposed to IVA or DIG).

RESULTS

During a median follow-up of 57.5 months, 1751 patients (74.1%) died, and 2151 (91.0%) were hospitalised for HF. CT-DIG or CT-IVA was associated with a lower all-cause mortality (DIG: HR = 0.86 [95% CI, 0.82-0.90], and IVA: HR = 0.88 [0.83-0.93]), cardiovascular mortality (DIG: HR = 0.84 [0.80-0.89] and IVA: HR = 0.83 [0.78-0.89]), hospitalisation (DIG: HR = 0.86 [0.83-0.89] and IVA: HR = 0.87 [0.83-0.91]) and 30-day readmission (DIG: HR = 0.84 [0.79-0.90] and IVA: HR = 0.88 [0.79-0.95]), after adjustment for cardiovascular comorbidity, and other potential confounders. These associations with the prognosis of HFrEF did not differ between patients who CT-DIG and those who CT-IVA.

CONCLUSION

Commencing therapy with digoxin or with ivabradine is associated with an improved prognosis of patients with HFrEF.

Ivabradine improves left ventricular twist and untwist during chronic hypertension

BACKGROUND

Left ventricular (LV) dysfunction develops during LV hypertrophy and particularly during tachycardia. Thus we investigated the effects of heart rate (HR) reduction with ivabradine, an I_f-channel blocker, on LV twist and untwist which represents myocardial deformation occurring during the overall systole and diastole and therefore provide valuable evaluation of global LV systolic and diastolic function.

METHODS

Eight chronically instrumented pigs receiving continuous angiotensin II infusion during 28days to induce chronic hypertension and LV hypertrophy. Measurements were performed at Days 0 and 28 after stopping angiotensin II infusion in the presence and absence of ivabradine.

RESULTS

At Day 0, reducing HR from 75±3 to 55±2beats/min with ivabradine did not affect LV twist but slowed LV untwist along with an increase in LV end-diastolic pressure. At Day 28, LV posterior and septal wall thickness as well as the estimated LV mass increased, indicating LV hypertrophy. LV twist and untwist were significantly reduced by 33±4% from 16±1° and 32±6% from -154±9°/s, respectively, showing global LV systolic and diastolic dysfunction. In this context, ivabradine decreased HR by 25% from 86±5beats/min and significantly improved LV twist from 11±1 to 14±1° and LV untwist from -104±8 to -146±5°/s.

CONCLUSIONS

Administration of ivabradine during chronic hypertension and LV hypertrophy improved LV twist and untwist. This further supports the beneficial effect of this drug on both LV systolic and diastolic function during the development of LV hypertrophy.

Kir2.1 channels set two levels of resting membrane potential with inward rectification

Strong inward rectifier K⁺ channels (Kir2.1) mediate background K⁺ currents primarily responsible for maintenance of resting membrane potential. Multiple types of cells exhibit two levels of resting membrane potential. Kir2.1 and K2P1 currents counterbalance, partially accounting for the phenomenon of human cardiomyocytes in subphysiological extracellular K⁺ concentrations or pathological hypokalemic conditions. The mechanism of how Kir2.1 channels contribute to the two levels of resting membrane potential in different types of cells is not well understood. Here we test the hypothesis that Kir2.1 channels set two levels of resting membrane potential with inward rectification. Under hypokalemic conditions, Kir2.1 currents counterbalance HCN2 or HCN4 cation currents in CHO cells that heterologously express both channels, generating N-shaped current-voltage relationships that cross the voltage axis three times and reconstituting two levels of resting membrane potential. Blockade of HCN channels eliminated the phenomenon in K2P1-deficient Kir2.1-expressing human cardiomyocytes derived from induced pluripotent stem cells or CHO cells expressing both Kir2.1 and HCN2 channels. Weakly inward rectifier Kir4.1 or inward rectification-deficient Kir2.1•E224G mutant channels do not set such two levels of resting membrane potential when co-expressed with HCN2 channels in CHO cells or when overexpressed in human cardiomyocytes derived from induced pluripotent stem cells. These findings demonstrate a common mechanism that Kir2.1 channels set two levels of resting membrane potential with inward rectification by balancing inward currents through different cation channels such as hyperpolarization-activated HCN channels or hypokalemia-induced K2P1 leak channels.

Influence of propafenone on the anticonvulsant activity of various novel antiepileptic drugs in the mouse maximal electroshock model

BACKGROUND

The main mechanism of action of propafenone (antiarrhythmic drug) involves the inhibition of the fast inward sodium current during phase 0 of the action potential. Sodium channel-blocking activity is also characteristic for some antiepileptic drugs. Therefore, it could be assumed that propafenone may also affect seizures. In the present study, we evaluated the effect of propafenone on the protective effect of oxcarbazepine, lamotrigine, topiramate and pregabalin against the maximal electroshock-induced seizures in mice.

METHODS

Anticonvulsant activity of propafenone was assessed with the maximal electroshock seizure threshold (MEST) test. Influence of propafenone on the anticonvulsant activity of antiepileptic drugs was estimated in the mouse maximal electroshock model (MES). Drug-related adverse effects were determined in the chimney test (motor coordination) and passive-avoidance task (long-term memory). Brain concentrations of antiepileptics were assessed by fluorescence polarization immunoassay.

RESULTS

Propafenone at doses 60-90mg/kg significantly increased the threshold of seizures, in turn at doses 5-50mg/kg did not affect this parameter. Administration of propafenone at the subthreshold dose of 50mg/kg increased antielectroshock activity of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine. As regards adverse effects, propafenone alone and in combination with antiepileptic drugs did not significantly impair motor coordination or long-term memory in mice. Propafenone (50mg/kg) significantly increased the brain level of pregabalin. Brain concentrations of topiramate and oxcarbazepine were not affected.

CONCLUSION

Our findings show that propafenone has own anticonvulsant action and enhances efficacy of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine, at least in experimental condition.

Phosphodiesterases 3 and 4 Differentially Regulate the Funny Current, If, in Mouse Sinoatrial Node Myocytes

Cardiac pacemaking, at rest and during the sympathetic fight-or-flight response, depends on cAMP (3',5'-cyclic adenosine monophosphate) signaling in sinoatrial node myocytes (SAMs). The cardiac "funny current" (I_f) is among the cAMP-sensitive effectors that drive pacemaking in SAMs. I_f is produced by hyperpolarization-activated, cyclic nucleotide-sensitive (HCN) channels. Voltage-dependent gating of HCN channels is potentiated by cAMP, which acts either by binding directly to the channels or by activating the cAMP-dependent protein kinase (PKA), which phosphorylates them. PKA activity is required for signaling between β adrenergic receptors (βARs) and HCN channels in SAMs but the mechanism that constrains cAMP signaling to a PKA-dependent pathway is unknown. Phosphodiesterases (PDEs) hydrolyze cAMP and form cAMP signaling domains in other types of cardiomyocytes. Here we examine the role of PDEs in regulation of I_f in SAMs. I_f was recorded in whole-cell voltage-clamp experiments from acutely-isolated mouse SAMs in the absence or presence of PDE and PKA inhibitors, and before and after βAR stimulation. General PDE inhibition caused a PKA-independent depolarizing shift in the midpoint activation voltage (V_1/2) of I_f at rest and removed the requirement for PKA in βAR-to-HCN signaling. PDE4 inhibition produced a similar PKA-independent depolarizing shift in the V_1/2 of I_f at rest, but did not remove the requirement for PKA in βAR-to-HCN signaling. PDE3 inhibition produced PKA-dependent changes in I_f both at rest and in response to βAR stimulation. Our results suggest that PDE3 and PDE4 isoforms create distinct cAMP signaling domains that differentially constrain access of cAMP to HCN channels and establish the requirement for PKA in signaling between βARs and HCN channels in SAMs.

Advances in heart failure: a review of biomarkers, emerging pharmacological therapies, durable mechanical support and telemonitoring

The purpose of this review is to provide an overview of diagnosis, prognosis and management of heart failure (HF) with reduced ejection fraction (HFrEF). Specifically, this review is divided into three sections. The first section will address biomarkers. The discovery of biomarkers has allowed further understanding of the pathophysiology of HF and provides insight into potential therapeutic targets. This review will focus on novel applications of natriuretic peptides (NPs) in clinical trials. Next, emerging biomarkers of HF, such as ST2, galectin-3 and copeptin, will be discussed. The second section aims to highlight HF therapies, including novel drugs and durable devices. The last section will review home haemodynamic monitoring and mobile health. We aim to provide context for the understanding of novel diagnostic and therapeutic advances in HF that are still in phase II or III trials, and have yet to become widely available.

Cyclic Purine and Pyrimidine Nucleotides Bind to the HCN2 Ion Channel and Variably Promote C-Terminal Domain Interactions and Opening

Cyclic AMP is thought to facilitate the opening of the HCN2 channel by binding to a C-terminal domain and promoting or inhibiting interactions between subunits. Here, we correlated the ability of cyclic nucleotides to promote interactions of isolated HCN2 C-terminal domains in solution with their ability to facilitate channel opening. Cyclic IMP, a cyclic purine nucleotide, and cCMP, a cyclic pyrimidine nucleotide, bind to a C-terminal domain containing the cyclic nucleotide-binding domain but, in contrast to other cyclic nucleotides examined, fail to promote its oligomerization, and produce only modest facilitation of opening of the full-length channel. Comparisons between ligand bound structures identify a region between the sixth and seventh β strands and the distal C helix as important for facilitation and tight binding. We propose that promotion of interactions between the C-terminal domains by a given ligand contribute to its ability to facilitate opening of the full-length channel.

A Single Protein Kinase A or Calmodulin Kinase II Site Does Not Control the Cardiac Pacemaker Ca2+ Clock

BACKGROUND

Fight or flight heart rate (HR) increases depend on protein kinase A (PKA)- and calmodulin kinase II (CaMKII)-mediated enhancement of Ca(2+) uptake and release from sarcoplasmic reticulum (SR) in sinoatrial nodal cells (SANC). However, the impact of specific PKA and CaMKII phosphorylation sites on HR is unknown.

METHODS AND RESULTS

We systematically evaluated validated PKA and CaMKII target sites on phospholamban and the ryanodine receptor using genetically modified mice. We found that knockin alanine replacement of ryanodine receptor PKA (S2808) or CaMKII (S2814) target sites failed to affect HR responses to isoproterenol or spontaneous activity in vivo or in SANC. Similarly, selective mutation of phospholamban amino acids critical for enhancing SR Ca(2+) uptake by PKA (S16) or CaMKII (T17) to alanines did not affect HR in vivo or in SANC. In contrast, CaMKII inhibition by expression of AC3-I has been shown to slow SANC rate responses to isoproterenol and decrease SR Ca(2+) content. Phospholamban deficiency rescued SR Ca(2+) content and SANC rate responses to isoproterenol in mice with AC3-I expression, suggesting that CaMKII affects HR by modulation of SR Ca(2+) content. Consistent with this, mice expressing a superinhibitory phospholamban mutant had low SR Ca(2+) content and slow HR in vivo and in SANC.

CONCLUSIONS

SR Ca(2+) depletion reduces HR and SR Ca(2+) repletion restores physiological SANC rate responses, despite CaMKII inhibition. PKA and CaMKII do not affect HR by a unique target site governing SR Ca(2+) uptake or release. HR acceleration may require an SR Ca(2+) content threshold.

Hyperpolarization-activated cation and T-type calcium ion channel expression in porcine and human renal pacemaker tissues

Renal pacemaker activity triggers peristaltic upper urinary tract contractions that propel waste from the kidney to the bladder, a process prone to congenital defects that are the leading cause of pediatric kidney failure. Recently, studies have discovered that hyperpolarization-activated cation (HCN) and T-type calcium (TTC) channel conductances underlie murine renal pacemaker activity, setting the origin and frequency and coordinating upper urinary tract peristalsis. Here, we determined whether this ion channel expression is conserved in the porcine and human urinary tracts, which share a distinct multicalyceal anatomy with multiple pacemaker sites. Double chromagenic immunohistochemistry revealed that HCN isoform 3 is highly expressed at the porcine minor calyces, the renal pacemaker tissues, whereas the kidney and urinary tract smooth muscle lacked this HCN expression. Immunofluorescent staining demonstrated that HCN(+) cells are integrated within the porcine calyx smooth muscle, and that they co-express TTC channel isoform Cav3.2. In humans, the anatomic structure of the minor calyx pacemaker was assayed via hematoxylin and eosin analyses, and enabled the visualization of the calyx smooth muscle surrounding adjacent papillae. Strikingly, immunofluorescence revealed that HCN3(+) /Cav3.2(+) cells are also localized to the human minor calyx smooth muscle. Collectively, these data have elucidated a conserved molecular signature of HCN and TTC channel expression in porcine and human calyx pacemaker tissues. These findings provide evidence for the mechanisms that can drive renal pacemaker activity in the multi-calyceal urinary tract, and potential causes of obstructive uropathies.

Propafenone enhances the anticonvulsant action of classical antiepileptic drugs in the mouse maximal electroshock model

BACKGROUND

Antiarrhythmic and antiepileptic drugs share some mechanisms of actions. Therefore, possibility of interactions between these in epileptic patients with cardiac arrhythmias is quite considerable. Herein, we attempted to assess interactions between propafenone and four conventional antiepileptic drugs: carbamazepine, valproate, phenytoin and phenobarbital.

METHODS

Effects of propafenone on seizures were determined in the electroconvulsive threshold test in mice. Interactions between propafenone and antiepileptic drugs were estimated in the model of maximal electroshock. Motor coordination was evaluated in the chimney test, while long-term memory in the passive-avoidance task. Brain concentrations of antiepileptics were determined by fluorescence polarization immunoassay.

RESULTS

Propafenone up to 50mg/kg did not affect the electroconvulsive threshold, significantly enhancing this parameter at doses of 60-90mg/kg. Applied at its subthreshold doses, propafenone potentiated the antielectroshock action of all four tested classical antiepileptics: carbamazepine, valproate, phenytoin, and phenobarbital. Propafenone alone and in combinations with antiepileptics impaired neither motor performance nor long-term memory in mice. Propafenone did not change brain concentration of phenytoin and phenobarbital; however, it significantly decreased brain levels of carbamazepine and increased those of valproate.

CONCLUSIONS

Propafenone exhibits its own anticonvulsant effect and enhances the action of classical antiepileptic drugs against electrically induced convulsions in mice. Further investigations are required to determine the effect of propafenone on antiepileptic therapy in humans.

HCN Channels Modulators: The Need for Selectivity

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, the molecular correlate of the hyperpolarization-activated current (If/Ih), are membrane proteins which play an important role in several physiological processes and various pathological conditions. In the Sino Atrial Node (SAN) HCN4 is the target of ivabradine, a bradycardic agent that is, at the moment, the only drug which specifically blocks If. Nevertheless, several other pharmacological agents have been shown to modulate HCN channels, a property that may contribute to their therapeutic activity and/or to their side effects. HCN channels are considered potential targets for developing drugs to treat several important pathologies, but a major issue in this field is the discovery of isoform-selective compounds, owing to the wide distribution of these proteins into the central and peripheral nervous systems, heart and other peripheral tissues. This survey is focused on the compounds that have been shown, or have been designed, to interact with HCN channels and on their binding sites, with the aim to summarize current knowledge and possibly to unveil useful information to design new potent and selective modulators.

New pharmacologic interventions to increase cardiac contractility: challenges and opportunities

PURPOSE OF REVIEW

The most extensively studied inotropic agents in patients with heart failure are phosphodiesterase (PDE) 3 inhibitors, which increase contractility by raising intracellular cyclic adenosine monophosphate content. In clinical trials, the inotropic benefits of these agents have been outweighed by an increase in sudden cardiac death. Here, I review recent findings that help explain what are likely to be distinct mechanisms involved in the beneficial and adverse effects of PDE3 inhibition.

RECENT FINDINGS

The proapoptotic consequences of PDE3 inhibition are becoming more apparent. Moreover, it has also become clear that individual PDE3 isoforms in cardiac myocytes are selectively regulated to interact with different proteins in different intracellular compartments. The beneficial and adverse effects of PDE3 inhibition may thus be attributable to the inhibition of different isoforms in different intracellular domains. In particular, PDE3A1 has been shown to interact directly with sarcoplasmic/endoplasmic reticulum Ca ATPase (SERCA2) in the sarcoplasmic reticulum through a phosphorylation of a site in its unique N-terminal domain, making it possible that this isoform can be selectively targeted to increase intracellular Ca cycling.

SUMMARY

Conventional PDE3 inhibitors target several functionally distinct isoforms of these enzymes. Isoform-selective and/or compartment-selective targeting of PDE3, through its protein-protein interactions, may produce the inotropic benefits of PDE3 inhibition without the adverse consequences.

Spontaneous ventricular tachyarrhythmias in β2-adrenoceptor transgenic mice in relation to cardiac interstitial fibrosis

Myocardial fibrosis is regarded as a pivotal proarrhythmic substrate, but there have been no comprehensive studies showing a correlation between the severity of fibrosis and ventricular tachyarrhythmias (VTAs). Our purpose was to document this relationship in a transgenic (TG) strain of mice with fibrotic cardiomyopathy. TG mice with cardiac overexpression of β2-adrenoceptors (β2-AR mice) and non-TG (NTG) littermates were studied at 4-12 mo of age. VTA was quantified by ECG telemetry. The effect of pharmacological blockade of β2-ARs on VTA was examined. Myocardial collagen content was determined by hydroxyproline assay. NTG and TG mice displayed circadian variation in heart rate, which was higher in TG mice than in NTG mice (P <0.05). Frequent spontaneous ventricular ectopic beats (VEBs) and ventricular tachycardia (VT) were prominent in TG mice but not present in NTG mice. The frequency of VEB and VT episodes in TG mice increased with age (P < 0.01). Ventricular collagen content was greater in TG mice than in NTG mice (P <0.001) and correlated with age (r = 0.71, P < 0.01). The number of VEBs or VT episodes correlated with age (r = 0.83 and r = 0.73) and the content of total or cross-linked collagen (r = 0.62∼0.66, all P <0.01). While having no effect in younger β2-TG mice, β2-AR blockade reduced the frequency of VTA in old β2-TG mice with more severe fibrosis. In conclusion, β2-TG mice exhibit interstitial fibrosis and spontaneous onset of VTA, becoming more severe with aging. The extent of cardiac fibrosis is a major determinant for both the frequency of VTA and proarrhythmic action of β2-AR activation.

Altered expression of hyperpolarization-activated cyclic nucleotide-gated channels and microRNA-1 and -133 in patients with age-associated atrial fibrillation

Hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels mediate pacemaker currents in the atrium. The microRNA (miR) families miR-1 and miR-133 regulate the expression of multiple genes involved in myocardial function, including HCN channels. It was hypothesized that age‑dependent changes in HCN2, HCN4, miR‑1 and miR‑133 expression may contribute to age‑associated atrial fibrillation, and therefore the correlation between expression levels, among adult (≤65 years) and aged patients (≥65 years), and sinus rhythm was determined. Right atrial appendage samples were collected from 60 patients undergoing coronary artery bypass grafting. Reverse transcription-quantitative polymerase chain reaction (PCR) and western blot analyses were performed in order to determine target RNA and protein expression levels. Compared with aged patients with sinus rhythm, aged patients with atrial fibrillation exhibited significantly higher HCN2 and HCN4 channel mRNA and protein expression levels (P<0.05), but significantly lower expression levels of miR‑1 and miR‑133 (P<0.05). In addition, aged patients with sinus rhythm exhibited significantly higher expression levels of HCN2 and HCN4 channel mRNA and protein (P<0.05), but significantly lower expression levels of miR‑1 and ‑133 (P<0.05), compared with those of adult patients with sinus rhythm. Expression levels of HCN2 and HCN4 increased with age, and a greater increase was identified in patients with age‑associated atrial fibrillation compared with that in those with aged sinus rhythm. These electrophysiological changes may contribute to the induction of ectopic premature beats that trigger atrial fibrillation.

Targeting the sarcomere to correct muscle function

Various human diseases can disrupt the balance between muscle contraction and relaxation. Sarcomeric modulators can be used to readjust this balance either indirectly by intervening in signalling pathways or directly through interaction with the muscle proteins that control contraction. Such agents represent a novel approach to treating any condition in which striated muscle function is compromised, including heart failure, cardiomyopathies, skeletal myopathies and a wide range of neuromuscular conditions. Here, we review agents that modulate the mechanical function of the sarcomere, focusing on emerging compounds that target myosin or the troponin complex.

Heart failure and atrial fibrillation: from basic science to clinical practice

Heart failure (HF) and atrial fibrillation (AF) are two growing epidemics associated with significant morbidity and mortality. They often coexist due to common risk factors and shared pathophysiological mechanisms. Patients presenting with both HF and AF have a worse prognosis and present a particular therapeutic challenge to clinicians. This review aims to appraise the common pathophysiological background, as well as the prognostic and therapeutic implications of coexistent HF and AF.

Priority Setting, Cost-Effectiveness, and the Affordable Care Act

The Affordable Care Act (ACA) may be the most important health law statute in American history, yet much of the most prominent legal scholarship examining it has focused on the merits of the court challenges it has faced rather than delving into the details of its priority-setting provisions. In addition to providing an overview of the ACA's provisions concerning priority setting and their developing interpretations, this Article attempts to defend three substantive propositions. First, I argue that the ACA is neither uniformly hostile nor uniformly friendly to efforts to set priorities in ways that promote cost and quality. Second, I argue that the ACA does not take a single, unified approach to priority setting; rather, its guidance varies depending on the aspect of the healthcare system at issue (Patient Centered Outcomes Research Institute, Medicare, essential health benefits) and the factors being excluded from priority setting (age, disability, life expectancy). Third, I argue that cost-effectiveness can be achieved within the ACA's constraints, but that doing so will require adopting new approaches to cost-effectiveness and priority setting. By limiting the use of standard cost-effectiveness analysis, the ACA makes the need for workable rivals to cost-effectiveness analysis a pressing practical concern rather than a mere theoretical worry.

A di-arginine ER retention signal regulates trafficking of HCN1 channels from the early secretory pathway to the plasma membrane

Hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels carry I_h, which contributes to neuronal excitability and signal transmission in the nervous system. Controlling the trafficking of HCN1 is an important aspect of its regulation, yet the details of this process are poorly understood. Here, we investigated how the C-terminus of HCN1 regulates trafficking by testing for its ability to redirect the localization of a non-targeted reporter in transgenic Xenopus laevis photoreceptors. We found that HCN1 contains an ER localization signal and through a series of deletion constructs, identified the responsible di-arginine ER retention signal. This signal is located in the intrinsically disordered region of the C-terminus of HCN1. To test the function of the ER retention signal in intact channels, we expressed wild type and mutant HCN1 in HEK293 cells and found this signal negatively regulates surface expression of HCN1. In summary, we report a new mode of regulating HCN1 trafficking: through the use of a di-arginine ER retention signal that monitors processing of the channel in the early secretory pathway.

Hemodynamic effects of Ivabradine in addition to dobutamine in patients with severe systolic dysfunction

BACKGROUND

Dobutamine induced tachycardia increases myocardial oxygen consumption and impairs ventricular filling. We hypothesized that Ivabradine may be efficient to control dobutamine induced tachycardia.

METHODS

We assessed the effects of Ivabradine in addition to dobutamine in stable heart failure (HF) patients (LVEF < 35%, n = 22, test population) and validated its effects in refractory cardiogenic shock patients (n = 9, validation population) with contraindication to cardiac assistance or transplant. In the test population (62 ± 17 years, LVEF = 24 ± 8%), systolic and diastolic function were assessed at rest and under dobutamine [10 γ/min], before and after Ivabradine [5mg per os]. In the validation population (54 ± 11 years, LVEF = 22 ± 7%), Ivabradine [5mg twice a day] was added to the dobutamine infusion.

RESULTS

In the test population, Ivabradine decreased heart rate [HR] at rest and during dobutamine echocardiography (-9 ± 8 bpm, P = 0.0004). The decrease in HR was associated with a decrease in cardiac power output and an increase in diastolic duration at rest (+ 74 ± 67 ms, P = 0.0002), and during dobutamine infusion (+ 75 ± 67 ms, P < 0.0001). Change in LVEF during dobutamine was greater after Ivabradine treatment than before (+ 7.2 ± 4.7% vs. + 3.6 ± 4.2%, P = 0.002). In the validation population, Ivabradine decreased HR (-18 ± 11 bpm, P = 0.008) and improved diastolic filling time (+ 67 ± 42 ms, P = 0.012) without decreasing cardiac output. At 24h, Ivabradine improved systolic blood pressure (+ 9 ± 5 mmHg, P = 0.007), daily urine output (+ 0.7 ± 0.5L, P = 0.008), oxygen balance (ΔScv02 = + 13 ± 15%, P = 0.010), and NT-pro BNP (-2270 ± 1912 pg/mL, P = 0.017). Finally, only 2/9 (22%) patients died whereas expected mortality determined from a historical cohort was 78% (P = 0.017).

CONCLUSION

This pilot study demonstrates the safety and potential benefit of a HR lowering agent in cardiogenic shock.

Diet-dependent modulation of gastro-oesphageal vagal afferent mechanosensitivity by endogenous nitric oxide

Neuronal nitric oxide (NO) plays an important role in gastric motor activity and modulates the mechanosensitivity of gastro-oesophageal vagal afferents. Effects of NO on food intake are dependent on feeding status. We sought to determine the effect of NO on gastro-oesophageal vagal afferent activity in the normally fed and food-restricted states and the second messenger pathways mediating these effects. Eight week old female C56BL/6 mice were fed ad libitum or food restricted for 14 h. An in vitro preparation was used to determine the functional effects of NO and the second messenger pathways involved. Expression of NO signal transduction molecules in vagal afferents was determined by reverse-transcription polymerase chain reaction (RT-PCR). Endogenous NO and the NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited vagal mucosal afferent responses to tactile stimuli in mice fed ad libitum. After a 14 h fast endogenous NO and SNAP potentiated tension and mucosal afferent responses to mechanical stimulation. The excitatory effect of NO was blocked by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin. After a 14 h fast expression of NADPH oxidase 2 (NOX2) mRNA in whole nodose ganglia was significantly reduced and the excitatory effect of NO on gastro-oesophageal vagal afferents was lost. Under fasting conditions the inhibitory effect of NO was blocked with the hyperpolarisation-activated cyclic nucleotide-gated (HCN) channel blocker ivabradine and mRNA expression of HCN3 in the nodose ganglia was elevated. In conclusion, the role of NO in the peripheral modulation of gastro-oesophageal vagal afferents is dynamic and dependent on feeding status.

Antiarrhythmic drugs and epilepsy

For a long time it has been suspected that epilepsy and cardiac arrhythmia may have common molecular background. Furthermore, seizures can affect function of the central autonomic control centers leading to short- and long-term alterations of cardiac rhythm. Sudden unexpected death in epilepsy (SUDEP) has most likely a cardiac mechanism. Common elements of pathogenesis create a basis for the assumption that antiarrhythmic drugs (AADs) may affect seizure phenomena and interact with antiepileptic drugs (AEDs). Numerous studies have demonstrated anticonvulsant effects of AADs. Among class I AADs (sodium channel blockers), phenytoin is an established antiepileptic drug. Propafenone exerted low anti-electroshock activity in rats. Lidocaine and mexiletine showed the anticonvulsant activity not only in animal models, but also in patients with partial seizures. Among beta-blockers (class II AADs), propranolol was anticonvulsant in models for generalized tonic-clonic and complex partial seizures, but not for myoclonic convulsions. Metoprolol and pindolol antagonized tonic-clonic seizures in DBA/2 mice. Timolol reversed the epileptiform activity of pentylenetetrazol (PTZ) in the brain. Furthermore, amiodarone, the representative of class III AADs, inhibited PTZ- and caffeine-induced convulsions in mice. In the group of class IV AADs, verapamil protected mice against PTZ-induced seizures and inhibited epileptogenesis in amygdala-kindled rats. Verapamil and diltiazem showed moderate anticonvulsant activity in genetically epilepsy prone rats. Additionally, numerous AADs potentiated the anticonvulsant action of AEDs in both experimental and clinical conditions. It should be mentioned, however, that many AADs showed proconvulsant effects in overdose. Moreover, intravenous esmolol and intra-arterial verapamil induced seizures even at therapeutic dose ranges.

A molecular signature of tissues with pacemaker activity in the heart and upper urinary tract involves coexpressed hyperpolarization-activated cation and T-type Ca2+ channels

Renal pacemakers set the origin and frequency of the smooth muscle contractions that propel wastes from the kidney to the bladder. Although congenital defects impairing this peristalsis are a leading cause of pediatric renal failure, the mechanisms underlying renal pacemaker activity remain unknown. Using ratiometric optical mapping and video microscopy, we discovered that hyperpolarization-activated cation (HCN) channel block with the specific anatagonist ZD7288 (30 μm; IC50) abolished the pacemaker depolarizations that initiate murine upper urinary tract peristalsis. Optical mapping and immunohistochemistry indicate that pacemaker potentials are generated by cells expressing HCN isoform-3, and that HCN3(+) cells are coupled to definitive smooth muscle via gap junctions. Furthermore, we demonstrate that HCN3(+) cells coexpress T-type Ca(2+) (TTC) channels and that TTC channel inhibition with R(-)efonidipine or NNC55-0396 decreased contractile frequency in a dose-dependent manner. Collectively, these data demonstrate that HCN3(+)/TTC(+) cells are the pacemakers that set the origin and rate of upper urinary tract peristalsis. These results reveal a conserved mechanism controlling autorhythmicity in 2 distinct muscle types, as HCN and TTC channels also mediate cardiac pacemaker activity. Moreover, these findings have translational applications, including the development of novel diagnostics to detect fetal urinary tract motility defects prior to renal damage.-Hurtado, R., Bub, G., Herzlinger, D. A molecular signature of tissues with pacemaker activity in the heart and upper urinary tract involves coexpressed hyperpolarization-activated cation and T-type Ca(2+) channels.

Management of pericarditis and myocarditis: could heart-rate-reducing drugs hold a promise?

Rest is usually recommended in acute pericarditis and acute myocarditis. Given that myocarditis often leads to hospitalization, this task seems easy to carry out in hospital practice; however, it could be a real challenge at home in daily life. Heart rate-lowering treatments (mainly beta-blockers) are usually recommended in case of acute myocarditis, especially in case of heart failure or arrhythmias, but level of proof remains weak. Calcium channel inhibitors and digoxin are sometimes proposed, albeit in limited situations. It is possible that rest or even heart rate-lowering treatments could help to manage these patients by preventing heart failure as well as by limiting "mechanical inflammation" and controlling arrhythmias, especially life-threatening ones. Whether heart rate has an effect on inflammation remains unclear. Several questions remain unsolved, such as the duration of such treatments, especially in light of new heart rate-lowering treatments, such as ivabradine. In this review, we discuss rest and heart-rate lowering medications for the treatment of pericarditis and myocarditis. We also highlight some work in experimental models that indicates the beneficial effects of such treatments for these conditions. Finally, we suggest certain experimental avenues, through the use of animal models and clinical studies, which could lead to improved management of these patients.

Hyperpolarization-activated current, If, in mathematical models of rabbit sinoatrial node pacemaker cells

A typical feature of sinoatrial (SA) node pacemaker cells is the presence of an ionic current that activates upon hyperpolarization. The role of this hyperpolarization-activated current, I_f, which is also known as the “funny current” or “pacemaker current,” in the spontaneous pacemaker activity of SA nodal cells remains a matter of intense debate. Whereas some conclude that I_f plays a fundamental role in the generation of pacemaker activity and its rate control, others conclude that the role of I_f is limited to a modest contribution to rate control. The ongoing debate is often accompanied with arguments from computer simulations, either to support one's personal view or to invalidate that of the antagonist. In the present paper, we review the various mathematical descriptions of I_f that have been used in computer simulations and compare their strikingly different characteristics with our experimental data. We identify caveats and propose a novel model for I_f based on our experimental data.