Diastolic Depolarization Research Articles

Characterization of the cellular components of mouse collecting lymphatic vessels reveals that lymphatic muscle cells are the innate pacemaker cells regulating lymphatic contractions.

Collecting lymphatic vessels (cLVs) exhibit spontaneous contractions with a pressure-dependent frequency, but the identity of the lymphatic pacemaker cell is still debated. By analogy to pacemakers in the GI and lower urinary tracts, proposed cLV pacemaker cells include interstitial cells of Cajal like cells (ICLC) or the lymphatic muscle (LMCs) cells themselves. Here we combined immunofluorescence and scRNAseq analyses with electrophysiological methods to examine the cellular constituents of the mouse cLV wall and assess whether any cell type exhibited morphological and functional processes characteristic of pacemaker cells: a continuous if not contiguous network integrated into the electrical syncytium; spontaneous Ca2+ transients; and depolarization-induced propagated contractions. We employed inducible Cre (iCre) mouse models routinely used to target these specific cell populations including: c-kitCreER T2 to target ICLC; PdgfrβCreER T2 to target pericyte-like cells; PdgfrαCreER ™ to target CD34+ adventitial cells and ICLC; and Myh11CreER T2 to target LMCs directly. These specific inducible Cre lines were crossed to the fluorescent reporter ROSA26mT/mG, the genetically encoded Ca2+ sensor GCaMP6f, and the light-activated cation channel rhodopsin2 (ChR2). c-KitCreER T2 labeled both a sparse population of LECs and round adventitial cells that responded to the mast cell activator compound 48-80. PdgfrβCreER T2 drove recombination in both adventitial cells and LMCs, limiting its power to discriminate a pericyte-specific population. PdgfrαCreER ™ labeled a large population of interconnected, oak leaf-shaped cells primarily along the adventitial surface of the vessel. Of these cells, only LMCs consistently, but heterogeneously, displayed spontaneous Ca2+ events during the diastolic period of the contraction cycle, and whose frequency was modulated in a pressure-dependent manner. Optogenetic depolarization through the expression of ChR2 under control of Myh11CreER T2 , but not PdgfrαCreER ™ or c-KitCreER T2 , resulted in propagated contractions upon photo-stimulation. Membrane potential recordings in LMCs demonstrated that the rate of diastolic depolarization significantly correlated with contraction frequency. These findings support the conclusion that LMCs, or a subset of LMCs, are responsible for mouse cLV pacemaking.

Calmodulin kinase II inhibition suppresses atrioventricular conduction by regulating intracellular Ca2+ homeostasis

BackgroundCa2+/calmodulin-dependent protein kinase II (CaMKII) inhibition decelerates atrioventricular node (AVN) conduction, providing a potential treatment of tachycardia. However, the effectiveness of CaMKII inhibition on tachycardia and its underlying mechanism remains unclear. ObjectiveWe aimed to assess the effectiveness of CaMKII inhibition in reducing ventricular rates during atrial fibrillation and to elucidate the underlying mechanism in affecting AVN electrophysiology. MethodsCardiac CaMKII inhibition (AC3-I) mice were used. Transesophageal atrial pacing was performed to evaluate AVN conduction function and to induce atrial fibrillation. Patch-clamp techniques were employed to record action potentials and ionic currents in AVN cells. Intracellular Ca2+ transients and sarcomere length measurements were obtained with the IonOptix system. Masson trichrome stain was used to evaluate fibrosis in the AVN region. Western blotting and immunofluorescence techniques were employed to detect connexin expression and localization. ResultsCaMKII inhibition decreased the ventricular rate during atrial fibrillation and isoproterenol-induced tachycardia. Esophageal electrocardiogram results from AC3-I mice showed longer AVN conduction than in wild-type mice. AN- and N-type AVN cells from AC3-I mice exhibited slower action potential frequencies and diastolic depolarization rates than those of wild-type mice. The study revealed that CaMKII inhibition reduced AVN cell sarcoplasmic reticulum (SR) Ca2+ content, Ca2+ release rate from the SR during diastole, Ca2+ transient amplitude, and SR Ca2+ uptake rate. In addition, CaMKII inhibition prolonged the sarcomere diastole duration and enhanced the sensitivity of sarcomeres to Ca2+. ConclusionCaMKII inhibition effectively decreases the ventricular rate during atrial fibrillation and tachycardia by slowing down AVN conduction through suppressing Ca2+ overload in AVN cells.

Modulation of Spontaneous Action Potential Rate by Inositol Trisphosphate in Myocytes from the Rabbit Atrioventricular Node.

The atrioventricular node (AVN) is a key component of the cardiac conduction system and takes over pacemaking of the ventricles if the sinoatrial node fails. IP3 (inositol 1,4,5 trisphosphate) can modulate excitability of myocytes from other regions of the heart, but it is not known whether IP3 receptor (IP3-R) activation modulates AVN cell pacemaking. Consequently, this study investigated effects of IP3 on spontaneous action potentials (APs) from AVN cells isolated from rabbit hearts. Immunohistochemistry and confocal imaging demonstrated the presence of IP3-R2 in isolated AVN cells, with partial overlap with RyR2 ryanodine receptors seen in co-labelling experiments. In whole-cell recordings at physiological temperature, application of 10 µM membrane-permeant Bt3-(1,4,5)IP3-AM accelerated spontaneous AP rate and increased diastolic depolarization rate, without direct effects on ICa,L, IKr, If or INCX. By contrast, application via the patch pipette of 5 µM of the IP3-R inhibitor xestospongin C led to a slowing in spontaneous AP rate and prevented 10 µM Bt3-(1,4,5)IP3-AM application from increasing the AP rate. UV excitation of AVN cells loaded with caged-IP3 led to an acceleration in AP rate, the magnitude of which increased with the extent of UV excitation. 2-APB slowed spontaneous AP rate, consistent with a role for constitutive IP3-R activity; however, it was also found to inhibit ICa,L and IKr, confounding its use for studying IP3-R. Under AP voltage clamp, UV excitation of AVN cells loaded with caged IP3 activated an inward current during diastolic depolarization. Collectively, these results demonstrate that IP3 can modulate AVN cell pacemaking rate.

Caveolar Compartmentalization of Pacemaker Signaling is Required for Stable Rhythmicity of Sinus Nodal Cells and is Disrupted in Heart Failure.

Heart rhythm relies on complex interactions between electrogenic membrane proteins and intracellular Ca2+ signaling in sinoatrial node (SAN) myocytes; however, mechanisms underlying the functional organization of proteins involved in SAN pacemaking and its structural foundation remain elusive. Caveolae are nanoscale, plasma membrane pits that compartmentalize various ion channels and transporters, including those involved in SAN pacemaking, via binding with the caveolin-3 scaffolding protein, but the precise role of caveolae in cardiac pacemaker function is unknown. Our objective was to determine the role of caveolae in SAN pacemaking and dysfunction (SND). Biochemical co-purification, in vivo electrocardiogram monitoring, ex vivo optical mapping, in vitro confocal Ca2+ imaging, and immunofluorescent and electron microscopy analyses were performed in wild type, cardiac-specific caveolin-3 knockout, and 8-weeks post-myocardial infarction heart failure (HF) mice. SAN tissue samples from donor human hearts were used for biochemical studies. We utilized a novel 3-dimensional single SAN cell mathematical model to determine the functional outcomes of protein nanodomain-specific localization and redistribution in SAN pacemaking. In both mouse and human SANs, caveolae compartmentalized HCN4, Cav1.2, Cav1.3, Cav3.1 and NCX1 proteins within discrete pacemaker signalosomes via direct association with caveolin-3. This compartmentalization positioned electrogenic sarcolemmal proteins near the subsarcolemmal sarcoplasmic reticulum (SR) membrane and ensured fast and robust activation of NCX1 by subsarcolemmal local SR Ca2+ release events (LCRs), which diffuse across ~15-nm subsarcolemmal cleft. Disruption of caveolae led to the development of SND via suppression of pacemaker automaticity through a 50% decrease of the L-type Ca2+ current, a negative shift of the HCN current (I f) activation curve, and a 40% reduction of Na+/Ca2+-exchanger function, along with ~2.3-times widening of the sarcolemma-SR distance. These changes significantly decreased the SAN depolarizing force, both during diastolic depolarization and upstroke phase, leading to bradycardia, sinus pauses, recurrent development of SAN quiescence, and significant increase in heart rate lability. Computational modeling, supported by biochemical studies, identified NCX1 redistribution to extra-caveolar membrane as the primary mechanism of SAN pauses and quiescence due to the impaired ability of NCX1 to be effectively activated by LCRs and trigger action potentials. HF remodeling mirrored caveolae disruption leading to NCX1-LCR uncoupling and SND. SAN pacemaking is driven by complex protein interactions within a nanoscale caveolar pacemaker signalosome. Disruption of caveolae leads to SND, potentially demonstrating a new dimension of SAN remodeling and providing a newly recognized target for therapy.

Ivabradine in Septic Shock: A Narrative Review.

In patients with septic shock, compensatory tachycardia initially serves to maintain adequate cardiac output and tissue oxygenation but may persist despite appropriate fluid and vasopressor resuscitation. This sustained elevation in heart rate and altered heart rate variability, indicative of autonomic dysfunction, is a well-established independent predictor of adverse outcomes in critical illness. Elevated heart rate exacerbates myocardial oxygen demand, reduces ventricular filling time, compromises coronary perfusion during diastole, and impairs the isovolumetric relaxation phase of the cardiac cycle, contributing to ventricular-arterial decoupling. This also leads to increased ventricular and atrial filling pressures, with a heightened risk of arrhythmias. Ivabradine, a highly selective inhibitor of the sinoatrial node's pacemaker current (If or "funny" current), mitigates heart rate by modulating diastolic depolarization slope without affecting contractility. By exerting a selective chronotropic effect devoid of negative inotropic properties, ivabradine shows potential for improving hemodynamics in septic shock patients with cardiac dysfunction. This review evaluates the plausible mechanisms and existing evidence regarding the utility of ivabradine in managing patients with septic shock.

Pacemaking in the lymphatic system.

Lymphatic collecting vessels exhibit spontaneous phasic contractions that are critical for lymph propulsion and tissue fluid homeostasis. This rhythmic activity is driven by action potentials conducted across the lymphatic muscle cell (LMC) layer to produce entrained contractions. The contraction frequency of a lymphatic collecting vessel displays exquisite mechanosensitivity, with a dynamic range from <1 to >20 contractions per minute. A myogenic pacemaker mechanism intrinsic to the LMCs was initially postulated to account for pressure-dependent chronotropy. Further interrogation into the cellular constituents of the lymphatic vessel wall identified non-muscle cell populations that shared some characteristics with interstitial cells of Cajal, which have pacemaker functions in the gastrointestinal and lower urinary tracts, thus raising the possibility of a non-muscle cell pacemaker. However, recent genetic knockout studies in mice support LMCs and a myogenic origin of the pacemaker activity. LMCs exhibit stochastic, but pressure-sensitive, sarcoplasmic reticulum calcium release (puffs and waves) from IP3R1 receptors, which couple to the calcium-activated chloride channel Anoctamin 1, causing depolarisation. The resulting electrical activity integrates across the highly coupled lymphatic muscle electrical syncytia through connexin 45 to modulate diastolic depolarisation. However, multiple other cation channels may also contribute to the ionic pacemaking cycle. Upon reaching threshold, a voltage-gated calcium channel-dependent action potential fires, resulting in a nearly synchronous calcium global calcium flash within the LMC layer to drive an entrained contraction. This review summarizes the key ion channels potentially responsible for the pressure-dependent chronotropy of lymphatic collecting vessels and various mechanisms of IP3R1 regulation that could contribute to frequency tuning.

Analysis of changes in the action potential morphology of the mouse sinoatrial node true pacemaker cells during ontogenetic development in vitro and in silico.

Maturation of the mouse is accompanied by the increase in heart rate. However, the mechanisms underlying this process remain unclear. We performed an action potentials (APs) recordings in mouse sinoatrial node (SAN) true pacemaker cells and in silico analysis to clarify the mechanisms underlying pre-postnatal period heart rate changes. The APs of true pacemaker cells at different stages had similar configurations and dV/dtmax values. The cycle length, action potential duration (APD90), maximal diastolic potential (MDP), and AP amplitude decreased, meanwhile the velocity of diastolic depolarization (DDR) increased from E12.5 stage to adult. Using a pharmacological approach we found that in SAN true pacemaker cells ivabradine reduces the DDR and the cycle length significantly stronger in E12.5 than in newborn and adult mice, whereas the effects of Ni2+ and nifedipine were significantly stronger in adult mice. Computer simulations further suggested that the density of the hyperpolarization-activated pacemaker сurrent (If) decreased during development, whereas transmembrane and intracellular Ca2+ flows increased. The ontogenetic decrease in IK1 density from E12.5 to adult leads to depolarization of MDP to the voltage range in which calcium currents are activated, thereby shifting the balance from the "membrane-clock" to the "calcium-clock."

An Overview Of The Level Of Occupational Stress Of Anesthesiologists In The Surgical Room Of The Hospital In The Banyumas District Area

Exercise can indeed improve the quality of health if it is done in accordance with the rules or program. However, excessive exercise without considering the capacity of the organs, especially the heart, can result in disease, one of which is heart disease, namely heart rhythm disturbances. The death rate for athletes in 2022 will still be at 29% during competition. In this case, it proves that Holter monitoring (ambulatory ECG monitoring) is better in assessing heart rhythm in athletes. Arrhythmias in athletes are caused by inadequate cardiac remodeling, causing ion channels in the atrioventricular node to undergo immunohistochemical labeling, where L-type calcium (Ca2+) channels that carry inward current are known to play a major role in the diastolic depolarization of the atrioventricular node, and regulate the excitability and increase in axis potentiation. . In the important Ca2+ channels in the heart, a slowing process occurs which results in a barrier to atrioventricular node conduction. A decrease in the axis action potential phase process where calcium cannot replace potassium in cells results in electrical impulse disturbances.

IP3R1 underlies diastolic ANO1 activation and pressure-dependent chronotropy in lymphatic collecting vessels.

Pressure-dependent chronotropy of murine lymphatic collecting vessels relies on the activation of the Ca2+-activated chloride channel encoded by Anoctamin 1 (Ano1) in lymphatic muscle cells. Genetic ablation or pharmacological inhibition of ANO1 results in a significant reduction in basal contraction frequency and essentially complete loss of pressure-dependent frequency modulation by decreasing the rate of the diastolic depolarization phase of the ionic pacemaker in lymphatic muscle cells (LMCs). Oscillating Ca2+ release from sarcoendoplasmic reticulum Ca2+ channels has been hypothesized to drive ANO1 activity during diastole, but the source of Ca2+ for ANO1 activation in smooth muscle remains unclear. Here, we investigated the role of the inositol triphosphate receptor 1 (Itpr1; Ip3r1) in this process using pressure myography, Ca2+ imaging, and membrane potential recordings in LMCs of ex vivo pressurized inguinal-axillary lymphatic vessels from control or Myh11CreERT2;Ip3r1fl/fl (Ip3r1ismKO) mice. Ip3r1ismKO vessels had significant reductions in contraction frequency and tone but an increased contraction amplitude. Membrane potential recordings from LMCs of Ip3r1ismKO vessels revealed a depressed diastolic depolarization rate and an elongation of the plateau phase of the action potential (AP). Ca2+ imaging of LMCs using the genetically encoded Ca2+ sensor GCaMP6f demonstrated an elongation of the Ca2+ flash associated with an AP-driven contraction. Critically, diastolic subcellular Ca2+ transients were absent in LMCs of Ip3r1ismKO mice, demonstrating the necessity of IP3R1 activity in controlling ANO1-mediated diastolic depolarization. These findings indicate a critical role for IP3R1 in lymphatic vessel pressure-dependent chronotropy and contractile regulation.

A synthetic cardiac episode generator for explainable, pathology based action potential using heuristic polynomial signatures

Synthetic generation of biophysical signals caters to diverse applications of test vectors generation, exploration, data augmentation and machine learning training. Arrhythmiator, our contribution is a Python framework to generate synthetically, action potential for explain-ability and explore-ability of pathology (Arrhythmia) influenced cardiac episodes. In this work, we address the problem of large cardiac data-sets need, for deep learning models which are hindered by privacy laws by synthetic generation. We have addressed the problem of explainable computations, multi-scale, by virtue of novel stack sliced polynomial signatures, piece-wise linear and application context driven fitting/filtering in algorithmic framework. To account the problem of lack of standardised pathology specifications we developed PDL (Pathology descriptive language) portal which can be customised. We also addressed the challenge of high turnaround development cycle, inter-operate-ability computation issue by developing a single unified Python framework. To address computational costs, we leverage domain-specific heuristics through sliced state space control algorithms and a constant temporal resolution. We demonstrate the utility of our framework by generating two cases of Tachycardia, one influenced by sodium pump inhibition of spontaneous diastolic depolarisation (SDD) slope and other by ischaemic episode causing maximum diastolic depolarisation (MDP) shift. The concept of the pacemaker hierarchy is encompassed by developing pathology explainable computation as a structure (PECS). We showcase the flexibility and explore-ability of our framework through ease of filter connect profile plug-ins for action potential states upstroke and plateau. We validated the generated waveforms by developing trace and debug algorithms and a reference deviation score which marks the pathology influence. The validator module is a vectored attribute of action potential based on state space control algorithms.

ERG K+ channels mediate a major component of action potential repolarization in lymphatic muscle

Smooth muscle cells in the walls of collecting lymphatic vessels fire spontaneous action potentials (APs), which conduct rapidly over the muscle layer to initiate contractions that propel lymph. Several ion channels have been implicated in the currents underlying the AP spike and the preceding diastolic depolarization, but the molecular identities of K+ channels involved in AP repolarization are unknown. Based on previous studies of other rhythmically active smooth muscles, we hypothesized that ether-a-go-go related gene (ERG) K+ channels (Kv11) play an important role in repolarization of the AP in lymphatic muscle. Message for one or more ERG channel isoforms was detected by RT-PCR analysis of lymphatic vessels from mice, rats and humans. Membrane potential recordings in smooth muscle cells of rat and human lymphatics revealed that nanomolar concentrations of ERG-1 inhibitors (E-4031 and BeKm-1) prolonged the duration of the AP plateau (normally ~ 1 s in duration) and induced multiple spikes, whereas ERG-1 activators (ICA-105574 and RPR-260243) shortened the plateau and could completely inhibit spontaneous APs. At relatively high inhibitor concentrations, the AP plateau duration lasted as long as 24 s. ERG activators reversed the effects of ERG inhibitors and vice-versa. In pressure myograph studies, ERG channel inhibition prolonged the diastolic repolarization phase of the contraction cycle and reduced the frequency of spontaneous contractions. This is the first evidence for a specific K+ channel contributing to the AP in lymphatic muscle. Our results imply that lymphatic contractile dysfunction may occur in long QT type II patients with mutations that result in ERG channel loss-of-function or impaired trafficking of the channel to the cell membrane.

The Action Potential Clamp Technique as a Tool for Risk Stratification of Sinus Bradycardia Due to Loss-of-Function Mutations in HCN4: An In Silico Exploration Based on In Vitro and In Vivo Data.

These days, in vitro functional analysis of gene variants is becoming increasingly important for risk stratification of cardiac ion channelopathies. So far, such risk stratification has been applied to SCN5A, KCNQ1, and KCNH2 gene variants associated with Brugada syndrome and long QT syndrome types 1 and 2, respectively, but risk stratification of HCN4 gene variants related to sick sinus syndrome has not yet been performed. HCN4 is the gene responsible for the hyperpolarization-activated 'funny' current If, which is an important modulator of the spontaneous diastolic depolarization underlying the sinus node pacemaker activity. In the present study, we carried out a risk classification assay on those loss-of-function mutations in HCN4 for which in vivo as well as in vitro data have been published. We used the in vitro data to compute the charge carried by If (Qf) during the diastolic depolarization phase of a prerecorded human sinus node action potential waveform and assessed the extent to which this Qf predicts (1) the beating rate of the comprehensive Fabbri-Severi model of a human sinus node cell with mutation-induced changes in If and (2) the heart rate observed in patients carrying the associated mutation in HCN4. The beating rate of the model cell showed a very strong correlation with Qf from the simulated action potential clamp experiments (R2 = 0.95 under vagal tone). The clinically observed minimum or resting heart rates showed a strong correlation with Qf (R2 = 0.73 and R2 = 0.71, respectively). While a translational perspective remains to be seen, we conclude that action potential clamp on transfected cells, without the need for further voltage clamp experiments and data analysis to determine individual biophysical parameters of If, is a promising tool for risk stratification of sinus bradycardia due to loss-of-function mutations in HCN4. In combination with an If blocker, this tool may also prove useful when applied to human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) obtained from mutation carriers and non-carriers.

PDE4D mediates impaired β-adrenergic receptor signalling in the sinoatrial node in mice with hypertensive heart disease.

The sympathetic nervous system increases HR by activating β-adrenergic receptors (β-ARs) and increasing cAMP in sinoatrial node (SAN) myocytes while phosphodiesterases (PDEs) degrade cAMP. Chronotropic incompetence, the inability to regulate heart rate (HR) in response to sympathetic nervous system activation, is common in hypertensive heart disease; however, the basis for this is poorly understood. The objective of this study was to determine the mechanisms leading to chronotropic incompetence in mice with angiotensin II (AngII)-induced hypertensive heart disease. C57BL/6 mice were infused with saline or AngII (2.5 mg/kg/day for 3 weeks) to induce hypertensive heart disease. HR and SAN function in response to the β-AR agonist isoproterenol (ISO) were studied in vivo using telemetry and electrocardiography, in isolated atrial preparations using optical mapping, in isolated SAN myocytes using patch-clamping, and using molecular biology. AngII-infused mice had smaller increases in HR in response to physical activity and during acute ISO injection. Optical mapping of the SAN in AngII-infused mice demonstrated impaired increases in conduction velocity and altered conduction patterns in response to ISO. Spontaneous AP firing responses to ISO in isolated SAN myocytes from AngII-infused mice were impaired due to smaller increases in diastolic depolarization (DD) slope, hyperpolarization-activated current (If), and L-type Ca2+ current (ICa,L). These changes were due to increased localization of PDE4D surrounding β1- and β2-ARs in the SAN, increased SAN PDE4 activity, and reduced cAMP generation in response to ISO. Knockdown of PDE4D using a virus-delivered shRNA or inhibition of PDE4 with rolipram normalized SAN sensitivity to β-AR stimulation in AngII-infused mice. AngII-induced hypertensive heart disease results in impaired HR responses to β-AR stimulation due to up-regulation of PDE4D and reduced effects of cAMP on spontaneous AP firing in SAN myocytes.

Resistance of Embryonic Chick Atria to Inhibition of HCN-Channels and Components of the “Ca&lt;sup&gt;2+&lt;/sup&gt;-Clock”

Despite its medical importance, the cellular mechanisms activity and the contribution of various ion channels of embryonic heart automatism are not yet fully understood. In this study we investigated the effects of specific ion-channel inhibitors on the generation of action potentials in pacemaker cells of the right atrium in chicken embryos (HH36). We used microelectrode technique and evaluated the sensitivity of pacemaker cells to ivabradine (inhibitor of HCN-channels, through which the hyperpolarization-activated current, If), ryanodine (agonist of ryanodine receptors) and SN6 (inhibitor of Na+/Ca2+-exchange). It was found that the right atrium cells have a phase of slow diastolic depolarization. However, these cells were not sensitive to ivabradine (3 μM). We did not register significant changes in the electrophysiological parameters of action potentials.When ryanodine (1 μM) and SN6 (10 μM) were added to the perfusion solution, we observed similar effects: spontaneous rate the generation of action potential increased by 15%. Disturbance of rhythmic activity or disruption of the generation of electrical impulses were not observed in right atrial samples of chicken embryos. The obtained results allow us to conclude that, at this of embryonic development stage, HCN4-channels, ryanodine receptors, and the Na+/Ca2+-exchange are not decisive for maintaining the automatism of the right atrial cells in the chick embryo. We assume that the ion currents flowing through these channels are important in electrophysiology in adult animals, but they have a modulating function in the embryonic myocardium.

Perbandingan Efektivitas antara Ivabradin 5 mg dengan Bisoprolol 5 mg dalam Menjaga Kestabilan Hemodinamik pada Tindakan Laringoskopi Intubasi

Background: Laryngoscopy intubation can cause complications in the form of increased blood pressure and heart rate. This can be detrimental to patients with cardiovascular complications, increased intracranial pressure, and vascular anomalies. Various procedures are performed to stabilize hemodynamic fluctuations during laryngoscopy intubation, one of which is the administration of beta-blocking agents (Bisoprolol). In some studies, the administration of Bisoprolol can cause side effects such as hypotension and bradycardia. One drug considered to maintain hemodynamic stability in laryngoscopy intubation with minimal effects is the administration of Ivabradine, which works by regulating diastolic depolarization.&#x0D; Objective: To compare the effectiveness of Ivabradine 5 mg and Bisoprolol 5 mg in maintaining hemodynamic stability in laryngoscopy intubation.&#x0D; Methods: This double-blind randomized clinical trial was conducted at RSUP Dr. Wahidin Sudirohusodo Makassar in July-August 2022 with ethical qualifications from the Ethics Committee for Biomedical Research in Humans from the Faculty of Medicine, Hasanuddin University. The sample was the entire population that met the inclusion and exclusion criteria. The data were processed using SPSS 25. The analysis used paired T-test, Mann-Whitney, and Wilcoxon with a 95% confidence level (p&lt;0.005).&#x0D; Result: There was a significant decrease in the mean arterial pressure and decrease in heart rate after induction (T2-T0) in the Bisoprolol group (p&lt;0.05). The mean arterial pressure at T1-T0, T3-T0, T3-T2 did not statistically significant.&#x0D; Conclusion: Ivabradine 5 mg was more effective than Bisoprolol 5 mg in maintaining the stability of mean arterial pressure and heart rate in laryngoscopy intubation.

Insulin signaling is critical for sinoatrial node maintenance and function

Insulin and insulin-like growth factor 1 (IGF-1) signaling regulate cellular growth and glucose metabolism in the myocardium. However, their physiological role in the cells of the cardiac conduction system has never been explored. Therefore, we sought to determine the spatiotemporal function of insulin/IGF-1 receptors in the sinoatrial node (SAN). We generated cardiac conduction cell-specific inducible IGF-1 receptor (IGF-1R) knockout (KO) (CSIGF1RKO), insulin receptor (IR) KO (CSIRKO), and IR/IGF-1R double-KO (CSDIRKO) mice and evaluated their phenotypes. Telemetric electrocardiography revealed regular sinus rhythm in CSIGF1RKO mice, indicating that IGF-1R is dispensable for normal pacemaking. In contrast, CSIRKO and CSDIRKO mice exhibited profound sinus bradycardia. CSDIRKO mice showed typical sinus node dysfunction characterized by junctional rhythm and sinus pauses on electrocardiography. Interestingly, the lack of an insulin receptor in the SAN cells of CSIRKO and CSDIRKO mice caused sinus nodal fibrosis. Mechanistically, hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) protein expression significantly decreased in the CSIRKO and CSDIRKO mice relative to the controls. A patch-clamp study of the SAN cells of CSIRKO mice revealed a significant decrease in the funny current, which is responsible for spontaneous diastolic depolarization in the SAN. This result suggested that insulin receptor loss reduces the heart rate via downregulation of the HCN4 channel. Additionally, HCN1 expression was decreased in CSDIRKO mice, explaining their sinus node dysfunction. Our results reveal a previously unrecognized role of insulin/IGF-1 signaling in sinus node structural maintenance and pacemaker function.

Aging impairs the clustering and reduces the activity of the L-type calcium channels in the heart's pacemaker

Every heartbeat is initiated by a spontaneous electrical signal generated inside the cardiac pacemaker. In mammals, including humans, aging leads to the slowdown of the pacemaker rate, which can lead to pathological dysfunction and death. However, the mechanisms behind the age-associated slowdown of the pacemaker are not well understood. The automaticity of the pacemaker relies on a finely tuned balance of ionic currents, where L-type calcium channels play a central role. CaV1.2 and CaV1.3 channels are key players involved in the diastolic depolarization phase and action potential upstroke. In this project, we studied the effects of aging on CaV1.2 and CaV1.3 calcium channel function and regulation. Here we recorded the pacemaker activity and calcium currents on isolated spindle pacemaker cells with patch clamp. The clustering of LTCC has been highlighted with Super-resolution microscopy (GSD). We found that in mouse pacemaker cells, aging causes a reduction of calcium entry through L-type calcium channels, which is not accompanied by a reduction of protein expression. In turn, we found that aging disrupts calcium channel function at different levels. First, aging reduces the expression of L-type calcium channels at the plasma membrane. Second, aging reduces the clustering and nano-organization of L-type calcium channels. And finally, aging reduces the open channel probability, a sign of decreased functional coupling. Moreover, aging also alters the association between L-type calcium channels and beta-adrenergic receptors, altering the adrenergic modulation of the pacemaker cells. Next, we tested the hypothesis that reduced open probability of L-type calcium channels was responsible for a slower firing frequency. Interestingly, we found that the application of BayK was enough to restore intrinsic pacemaker rates in old cells to those levels observed in young cells. Overall, our findings provide evidence that the proper organization and function of L-type calcium channels is affected by aging and that this dysfunction contributes to the slowdown of pacemaker cells in old animals.

Human Sinoatrial Node Pacemaker Activity: Role of the Slow Component of the Delayed Rectifier K+ Current, IKs.

The pacemaker activity of the sinoatrial node (SAN) has been studied extensively in animal species but is virtually unexplored in humans. Here we assess the role of the slowly activating component of the delayed rectifier K+ current (IKs) in human SAN pacemaker activity and its dependence on heart rate and β-adrenergic stimulation. HEK-293 cells were transiently transfected with wild-type KCNQ1 and KCNE1 cDNA, encoding the α- and β-subunits of the IKs channel, respectively. KCNQ1/KCNE1 currents were recorded both during a traditional voltage clamp and during an action potential (AP) clamp with human SAN-like APs. Forskolin (10 µmol/L) was used to increase the intracellular cAMP level, thus mimicking β-adrenergic stimulation. The experimentally observed effects were evaluated in the Fabbri-Severi computer model of an isolated human SAN cell. Transfected HEK-293 cells displayed large IKs-like outward currents in response to depolarizing voltage clamp steps. Forskolin significantly increased the current density and significantly shifted the half-maximal activation voltage towards more negative potentials. Furthermore, forskolin significantly accelerated activation without affecting the rate of deactivation. During an AP clamp, the KCNQ1/KCNE1 current was substantial during the AP phase, but relatively small during diastolic depolarization. In the presence of forskolin, the KCNQ1/KCNE1 current during both the AP phase and diastolic depolarization increased, resulting in a clearly active KCNQ1/KCNE1 current during diastolic depolarization, particularly at shorter cycle lengths. Computer simulations demonstrated that IKs reduces the intrinsic beating rate through its slowing effect on diastolic depolarization at all levels of autonomic tone and that gain-of-function mutations in KCNQ1 may exert a marked bradycardic effect during vagal tone. In conclusion, IKs is active during human SAN pacemaker activity and has a strong dependence on heart rate and cAMP level, with a prominent role at all levels of autonomic tone.

Palmitoylation regulates the magnitude of HCN4-mediated currents in mammalian cells.

The sinoatrial node (SAN) and subsidiary pacemakers in the cardiac conduction system generate spontaneous electrical activity which is indispensable for electrical and therefore contractile function of the heart. The hyperpolarisation-activated cyclic nucleotide-gated channel HCN4 is responsible for genesis of the pacemaker "funny" current during diastolic depolarisation. S-palmitoylation, the reversible conjugation of the fatty acid palmitate to protein cysteine sulfhydryls, regulates the activity of key cardiac Na+ and Ca2+ handling proteins, influencing their membrane microdomain localisation and function. We investigated HCN4 palmitoylation and its functional consequences in engineered human embryonic kidney 293T cells as well as endogenous HCN4 in neonatal rat ventricular myocytes. HCN4 was palmitoylated in all experimental systems investigated. We mapped the HCN4 palmitoylation sites to a pair of cysteines in the HCN4 intracellular amino terminus. A double cysteine-to-alanine mutation CC93A/179AA of full length HCN4 caused a ∼67% reduction in palmitoylation in comparison to wild type HCN4. We used whole-cell patch clamp to evaluate HCN4 current (IHCN4) in stably transfected 293T cells. Removal of the two N-terminal palmitoylation sites did not significantly alter half maximal activation voltage of IHCN4 or the activation slope factor. IHCN4 was significantly larger in cells expressing wild type compared to non-palmitoylated HCN4 across a range of voltages. Phylogenetic analysis revealed that although cysteine 93 is widely conserved across all classes of HCN4 vertebrate orthologs, conservation of cysteine 179 is restricted to placental mammals. Collectively, we provide evidence for functional regulation of HCN4 via palmitoylation of its amino terminus in vertebrates. We suggest that by recruiting the amino terminus to the bilayer, palmitoylation enhances the magnitude of HCN4-mediated currents, but does not significantly affect the kinetics.

The paradigm shift: Heartbeat initiation without "the pacemaker cell".

The current dogma about the heartbeat origin is based on "the pacemaker cell," a specialized cell residing in the sinoatrial node (SAN) that exhibits spontaneous diastolic depolarization triggering rhythmic action potentials (APs). Recent high-resolution imaging, however, demonstrated that Ca signals and APs in the SAN are heterogeneous, with many cells generating APs of different rates and rhythms or even remaining non-firing (dormant cells), i.e., generating only subthreshold signals. Here we numerically tested a hypothesis that a community of dormant cells can generate normal automaticity, i.e., "the pacemaker cell" is not required to initiate rhythmic cardiac impulses. Our model includes 1) non-excitable cells generating oscillatory local Ca releases and 2) an excitable cell lacking automaticity. While each cell in isolation was not "the pacemaker cell", the cell system generated rhythmic APs: The subthreshold signals of non-excitable cells were transformed into respective membrane potential oscillations via electrogenic Na/Ca exchange and further transferred and integrated (computed) by the excitable cells to reach its AP threshold, generating rhythmic pacemaking. Cardiac impulse is an emergent property of the SAN cellular network and can be initiated by cells lacking intrinsic automaticity. Cell heterogeneity, weak coupling, subthreshold signals, and their summation are critical properties of the new pacemaker mechanism, i.e., cardiac pacemaker can operate via a signaling process basically similar to that of "temporal summation" happening in a neuron with input from multiple presynaptic cells. The new mechanism, however, does not refute the classical pacemaker cell-based mechanism: both mechanisms can co-exist and interact within SAN tissue.