Identifying the Evolutionary Building Blocks of the Cardiac Conduction System

The endothermic state of mammals and birds requires high heart rates to accommodate the high rates of oxygen consumption. These high heart rates are driven by very similar conduction systems consisting of an atrioventricular node that slows the electrical impulse and a His-Purkinje system that efficiently activates the ventricular chambers. While ectothermic vertebrates have similar contraction patterns, they do not possess anatomical evidence for a conduction system. This lack amongst extant ectotherms is surprising because mammals and birds evolved independently from reptile-like ancestors. Using conserved genetic markers, we found that the conduction system design of lizard (Anolis carolinensis and A. sagrei), frog (Xenopus laevis) and zebrafish (Danio rerio) adults is strikingly similar to that of embryos of mammals (mouse Mus musculus, and man) and chicken (Gallus gallus). Thus, in ectothermic adults, the slow conducting atrioventricular canal muscle is present, no fibrous insulating plane is formed, and the spongy ventricle serves the dual purpose of conduction and contraction. Optical mapping showed base-to-apex activation of the ventricles of the ectothermic animals, similar to the activation pattern of mammalian and avian embryonic ventricles and to the His-Purkinje systems of the formed hearts. Mammalian and avian ventricles uniquely develop thick compact walls and septum and, hence, form a discrete ventricular conduction system from the embryonic spongy ventricle. Our study uncovers the evolutionary building plan of heart and indicates that the building blocks of the conduction system of adult ectothermic vertebrates and embryos of endotherms are similar.     

Cardiac Effects of the Class III Antiarrhythmic Drugs Amiodarone and Nibentan

The effects of Amiodarone and Nibentan on the postextrasystolic and postrest reactions were studied with normal rat myocardium and (for Amiodarone only) with myocardial strips isolated from patients with coronary heart disease (CHD). One-third of the patient samples displayed spontaneous activity that could be effectively suppressed by Amiodarone. All other samples displayed postrest inotropic effects of two types, with 30 or 70% decreases in the parameters of the contraction-relaxation cycle. Amiodarone did not influence the reaction of the first type but increased the postrest inotropic response of the second type. Both Amiodarone and Nibentan decreased the postextrasystolic inotropic response of the normal rat myocardium and simultaneously increased the postextrasystolic contraction. In addition, these drugs nearly doubled postrest potentiation. In the patient myocardium samples, however, Amiodarone did not decrease the amplitude of the extrasystolic contraction but increased postextrasystolic potentiation. It was supposed that, in the myocardium of some CHD patients (as well as in the rat myocardium), Amiodarone increases the ability of the sarcoplasmic reticulum to accumulate calcium ions. The same was supposed for the effects observed for Nibentan in tests with the rat myocardium. This phenomenon may contribute to the suppression of abnormal activity of the myocardium and strengthen the direct antiarrhythmic effect of Amiodarone.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 4, 2005, pp. 113–118.Original Russian Text Copyright © 2005 by Ugdyzhekova, Afanas’ev, Lukavskaya, Popov.     

Incidence of Dispersion of Refractoriness and Cellular Coupling Resistance on Cardiac Reentries and Ventricular Fibrillation

We used computer simulations to study the possible role of the dispersion of cellular coupling, refractoriness or both, in the mechanisms underlying cardiac arrhythmias. Local ischemia was first assumed to induce cell to cell dispersion of the coupling resistance (Case 1), refractory period (Case 2), or both of them (Case 3). Our numerical experiments based on the van Capelle and Durrer model showed that vortices could not be induced by cell to cell variations. With cellular properties dispersed in a patchy way within the ischemic zone, a single activation wave could give rise to abnormal activities. This demonstrates the stability of the wave front under small inhomogeneities. Probabilities of reentry, estimated for the three cases cited above showed that a severe alteration of the coupling resistance may be an important factor in the genesis of reentry. Moreover, use of isochronal maps revealed that vortices were both stable and sustained with an alteration of the coupling alone or combined with a reduction of the action potential duration. Conversely, simulations with reduction of the refractoriness alone, inducing only transient patterns, could exhibit functionally determined reentries.     

Empirical Study of an Adaptive Multiscale Model for Simulating Cardiac Conduction

We modify and empirically study an adaptive multiscale model for simulating cardiac action potential propagation along a strand of cardiomyocytes. The model involves microscale partial differential equations posed over cells near the action potential upstroke and macroscale partial differential equations posed over the remainder of the tissue. An important advantage of the modified model of this paper is that, unlike our original model, it does not require perfect alignment between myocytes and the macroscale computational grid. We study the effects of gap-junctional coupling, ephaptic coupling, and macroscale grid spacing on the accuracy of the multiscale model. Our simulations reveal that the multiscale method accurately reproduces both the wavespeed and the waveform, including both upstroke and recovery, of fully microscale models. They also reveal that perfect alignment between myocytes and the macroscale grid is not necessary to reproduce the dynamics of a traveling action potential. Further, our simulations suggest that the macroscale grid spacing used in an adaptive multiscale model need not be much finer than the spatial width of an action potential. These results are demonstrated to hold under high, low, and zero gap-junctional coupling regimes.     

Effect of Ibutilide on the Canine Cardiac Conduction System

The objective of the study was to evaluate the effect of ibutilide on canine cardiac sinoatrial and atrioventricular nodes (AVNs). For this purpose, 18 mongrel dogs were injected intravenously with ibutilide and the changes in heart rate, sinus node recovery time, and AVN were measured. Our data show that ibutilide administration caused significant suppression of the sinus atrial node, the peak response time was 20?C30?min, and the heart rate was restored to pre-drug administration level. After receiving ibutilide, 1 animal had a 5?s sinus pause, and after 5?min of ibutilide administration, 1 dog showed 2:1 atrioventricular conduction. Therefore, it was concluded that ibutilide had a suppressive effect on the sinoatrial node and AVN.     

Normal Mode Analysis Theoretical and Applications to Biological and Chemical Systems.

The realization that many of the important biochemical phenomenaoccur in the micro- to millisecond timescale has resulted inthe need for computational methods that would extend beyondthe nanosecond regime that is currently accessible with explicit-solventmolecular dynamics simulations. The normal mode analysis method,initially developed in solid-phase physics, met that need byenabling the exploration of large scale collective motions thatoccur in systems ranging from small proteins and nucleic acidsto the bacterial ribosome. This method requires the derivationof eigenvectors and eigenvalues through the diagonalizationof the Hessian matrix, which is composed of mass-weighed secondderivatives of the potential energy function. The     

Ischemia-Related Subcellular Redistribution of Sodium Channels Enhances the Proarrhythmic Effect of Class I Antiarrhythmic Drugs: A Simulation Study

Background

Cardiomyocytes located at the ischemic border zone of infarcted ventricle are accompanied by redistribution of gap junctions, which mediate electrical transmission between cardiomyocytes. This ischemic border zone provides an arrhythmogenic substrate. It was also shown that sodium (Na⁺) channels are redistributed within myocytes located in the ischemic border zone. However, the roles of the subcellular redistribution of Na⁺ channels in the arrhythmogenicity under ischemia remain unclear.

Methods

Computer simulations of excitation conduction were performed in a myofiber model incorporating both subcellular Na⁺ channel redistribution and the electric field mechanism, taking into account the intercellular cleft potentials.

Results

We found in the myofiber model that the subcellular redistribution of the Na⁺ channels under myocardial ischemia, decreasing in Na⁺ channel expression of the lateral cell membrane of each myocyte, decreased the tissue excitability, resulting in conduction slowing even without any ischemia-related electrophysiological change. The conventional model (i.e., without the electric field mechanism) did not reproduce the conduction slowing caused by the subcellular Na⁺ channel redistribution. Furthermore, Na⁺ channel blockade with the coexistence of a non-ischemic zone with an ischemic border zone expanded the vulnerable period for reentrant tachyarrhythmias compared to the model without the ischemic border zone. Na⁺ channel blockade tended to cause unidirectional conduction block at sites near the ischemic border zone. Thus, such a unidirectional conduction block induced by a premature stimulus at sites near the ischemic border zone is associated with the initiation of reentrant tachyarrhythmias.

Conclusions

Proarrhythmia of Na⁺ channel blockade in patients with old myocardial infarction might be partly attributable to the ischemia-related subcellular Na⁺ channel redistribution.     

顺铂短期诱导人腺样囊性癌细胞NACC 产生耐药性的研究

目的:探讨人腭部涎腺腺样囊性癌细胞(NACC)经顺铂(DDP)短期诱导后耐药性产生情况及耐药机制。方法:采用恒定浓度DDP反复间歇诱导法诱导NACC细胞,获得耐药细胞NACC/DDP3,MTT法检测细胞耐药指数;实时荧光定量PCR检测存活蛋白(Survivin)及核苷酸切除修复交叉互补基因1(ERCC1)的mRNA表达;裸鼠右侧腋部皮下接种NACC及NACC/DDP3细胞,成瘤后将荷瘤裸鼠随机分为生理盐水对照组和DDP 2 mg·kg~(-1)组,比较2 mg·kg~(-1) DDP对两组荷瘤裸鼠的抑瘤率,HE染色观察肿瘤组织形态。结果:诱导后的NACC/DDP3对DDP耐药性增强,耐药指数为1.44;在NACC/DDP3细胞中,Survivin及ERCC1的mRNA表达明显上调,分别为亲本细胞的2.02(P0.01)和1.59(P0.05)倍;2 mg·kg~(-1) DDP对NACC组抑瘤率为(31.64±1.15)%,对NACC/DDP3组抑瘤率为(16.66±0.76)%,两组间差异具有统计学意义(P0.01),HE染色观察两组瘤体标本均符合腺样囊性癌实体型组织学表现。结论:NACC细胞经DDP短期诱导即产生一定耐药性,NACC/DDP3细胞中Survivin及ERCC1的mRNA表达上调,提示Survivin及ERCC1可能参与了腺样囊性癌细胞对DDP的耐药。相同剂量DDP对NACC/DDP3所建立的皮下移植瘤模型抑瘤率显著低于NACC组,提示NACC/DDP3接种到裸鼠体内仍具有耐药性,这将为体内研究耐药腺样囊性癌的治疗提供良好的平台。     

Effect of some Cardiac and Respiratory Drugs on Succinate-Cytochrome c Reductase

Succinate-cytochrome c reductase was inhibited in vitro and in vivo by phenobarbitone, aminophylline and neostigmine using both 2,6-dichlorophenolindophenol (DCIP) and cytochrome c (cyt c) as substrates. The enzyme was also activated by gallamine towards both substrates. In vitro, phenobarbitone and aminophylline inhibited the enzyme with respect to the reduction of DCIP and cyt c in a non-competitive manner with K_i values of 1.5 × 10^?5 and 5.7 × 10^?5 M, respectively. Moreover, neostigmine competitively inhibited the enzyme towards both substrates with K_i values of 1.36 × 10^?5 and 1.50 × 10^?5 M, respectively.     

氢气影响大鼠神经兴奋传导的研究

氢气是一种具有重要生物学功能的气体分子,可以用于神经退行性疾病、抑郁、睡眠障碍和毒瘾戒断症状等的治疗和改善,普遍认为和氢气的选择性抗氧化有关,但氢气对神经功能的调控机制尚不清楚。为了探究氢气对神经功能的调控机制,通过脑片膜片钳技术分别检测了氢瞬时作用大鼠大脑切片皮层神经细胞和饮用富氢水（8周）大鼠大脑切片皮层神经细胞的动作电位变化,以判断氢的干预是否能够影响神经兴奋的传导;利用液相色谱质谱联用仪（liquid chromatograph-mass spectrometer,LCMS）检测饮用富氢水（8周）大鼠大脑切片皮层神经递质的含量变化,以进一步探究氢气影响神经兴奋传导的具体机制。结果表明,氢气处理组与对照组相比大鼠皮层神经细胞的阈值电压、动作电位间隔和输入抗阻具有显著性差异（P<0.05）,氢气处理组静息膜电位升高,神经细胞爆发动作电位阈值升高,表明氢气可能对神经细胞膜离子通道的开放和关闭有影响,氢处理能够使皮层神经细胞兴奋性明显降低。大鼠在连续饮用富氢水8周后大脑皮层同样显现出兴奋性降低趋势,经LCMS测定,发现神经递质的含量没有明显变化。研究提示,氢气可能是通过改变细胞内外电荷差异变化或者直接影响神经细胞表面钠、钾等离子通道的打开或关闭,从而实现对神经细胞兴奋性的调节。     

Transient hypothyroidism in infants born to mothers with chronic thyroiditis--a nationwide study of twenty-three cases. The Transient Hypothyroidism Study Group

To define the difference in prognosis and the clinical features of transient neonatal hypothyroidism in infants born to mothers with chronic thyroiditis, we conducted a nationwide study of this condition. Sixteen mothers with chronic thyroiditis and twenty-three of their offspring with transient hypothyroidism were registered and reported in this paper. Five (group A) of twenty-two live infants showed physical, mental and/or psychomotor developmental delay (IQ below 80). No significant difference between TSH-binding inhibitor immunoglobulin (TBII) or thyroid-stimulation blocking antibody (TSBAb) activities in groups A and B (normal development) were noted. Moreover, there was no significant difference in thyroid function in the newborn period, ages at the start of thyroid medication or the dose and duration of treatment in the two groups. A striking difference observed between the two groups was the thyroid function of their mothers during pregnancy. In group A, four mothers were hypothyroid during pregnancy, and another mother discontinued thyroid medication in the last trimester and her baby was most delayed at the start thyroid medication. On the other hand, the mothers of only two of seventeen live cases in group B had mild hypothyroidism during pregnancy. There were two sets of siblings whose mother received inadequate treatment during the first pregnancy and adequate treatment during the second pregnancy. The psychomotor, physical and mental developmental delay were observed in their first babies. These findings suggested that maternal thyroid function during pregnancy might be an important factor in the prognosis of infants born to mothers with chronic thyroiditis.     

Construction of Defined Human Engineered Cardiac Tissues to Study Mechanisms of Cardiac Cell Therapy

Human cardiac tissue engineering can fundamentally impact therapeutic discovery through the development of new species-specific screening systems that replicate the biofidelity of three-dimensional native human myocardium, while also enabling a controlled level of biological complexity, and allowing non-destructive longitudinal monitoring of tissue contractile function. Initially, human engineered cardiac tissues (hECT) were created using the entire cell population obtained from directed differentiation of human pluripotent stem cells, which typically yielded less than 50% cardiomyocytes. However, to create reliable predictive models of human myocardium, and to elucidate mechanisms of heterocellular interaction, it is essential to accurately control the biological composition in engineered tissues. To address this limitation, we utilize live cell sorting for the cardiac surface marker SIRPα and the fibroblast marker CD90 to create tissues containing a 3:1 ratio of these cell types, respectively, that are then mixed together and added to a collagen-based matrix solution. Resulting hECTs are, thus, completely defined in both their cellular and extracellular matrix composition.Here we describe the construction of defined hECTs as a model system to understand mechanisms of cell-cell interactions in cell therapies, using an example of human bone marrow-derived mesenchymal stem cells (hMSC) that are currently being used in human clinical trials. The defined tissue composition is imperative to understand how the hMSCs may be interacting with the endogenous cardiac cell types to enhance tissue function. A bioreactor system is also described that simultaneously cultures six hECTs in parallel, permitting more efficient use of the cells after sorting.     

Effects of Ibutilide on Canine Cardiac Pacing Threshold and on Induction Rates of Atrial Fibrillation

This study aims to observe the effects of ibutilide on canine cardiac pacing threshold and on induction rates of atrial fibrillation. Eighteen mongrel dogs were anesthetized and administrated with ibutilide. The pacing thresholds and induction rates of atrial fibrillation were measured with and without ibutilide (10-min infusion dose was 0.10?mg?kg^?1, followed by a maintaining dose of 0.01?mg?min^?1 30?min later). This study found that ibutilide increases pacing thresholds in dogs. Moreover, there were significant differences between pacing thresholds with and without ibutilide (P?<?0.05). Further, ibutilide significantly reduces the induction rates of atrial fibrillation (P?<?0.05). Our findings indicate that pacing voltage changes should be closely monitored in patients taking anti-arrhythmic drugs, who are treated with cardiac stimulation or have undergone pacemaker implantation. We also found that ibutilide is an effective drug in preventing or controlling atrial fibrillation.     

水杨酸诱导小白菜抗霜霉病的作用研究

以小白菜(Brassica campestris ssp.chinesis L.)为材料,采用叶面喷洒的方法施用不同浓度水杨酸(Salicylic acid,SA),研究了SA小白菜对霜霉病的抗性诱导,并对经SA诱导后小白菜植株体内相关酶活性进行了研究.结果发现,在0.2～2.0 mmol·L-1的浓度范围内,随着SA浓度的增加,SA的诱导防治效果先增后减,1.0 mmol·L-1浓度为诱导抗性最适浓度.经SA诱导后,小白菜植株体内SOD、POD和PPO等酶活性也明显增强.     

Effect of Potassium on the Assimilate Conduction to Storage Tissue

The promoting effect of K+ on phloem transport has been shown by various authors for different plant species. This effect was also obtained in cases in which C0₂-assimilation was not improved by K+. Experiments with Ricinus communis provided evidence that K+ favoured the flux rate of phloem sap without diluting its content in organic and inorganic solutes. This all over effect results in higher flux rates of all phloem solutes. In this respect the long distance transport of sucrose, amino acids and Mg²+ is of particular interest. The long distance transport of these compounds was shown to be favoured by K+. Potassium is known to activate starch and protein synthezising enzymes involved in the metabolism of storage tissue. There is evidence, that also in cases of a suboptimum K+ supply, the K+ level in the storage tissue probably is still high enough to provide an optimum activation of the K+ requiring enzymes. For this reason it is unlikely that the favourable effect of K+ on phloem transport is related to processes in the physiological sink. It is more likely that K+ favours the phloem loading process. Indirectly K+ could promote the phloem loading process by improving the provision of energy (ATP). It is, however, also feasible that K+ acts more directly by being involved in the ATPase reaction which is supposed to drive the sucrose uptake of sieve tubes.     

铁皮石斛愈伤组织诱导研究

研究不同培养基和光照条件对铁皮石斛愈伤组织诱导的影响。结果表明,外植体直接接种于培养基上,最适宜培养条件是MS 5.92 g·L^-1＋2,4-D 5 mg·L^-1＋IAA 1.5 mg·L^-1＋KT 0.62 mg·L^-1＋蔗糖37.5 g·L^-1＋琼脂0.8% (pH 5.9～6.0),暗培养15 d后再光培养;外植体捣碎后平铺于培养基上,最适宜培养条件是MS 4.74 g·L^-1＋2,4-D 1 mg·L^-1＋IAA 1.5 mg·L^-1＋KT 0.25 mg·L^-1＋蔗糖30 g·L^-1＋琼脂0.8% (pH 5.9～6.0),25 ℃持续光培养。     

Reovirus Induction of and Sensitivity to Beta Interferon in Cardiac Myocyte Cultures Correlate with Induction of Myocarditis and Are Determined by Viral Core Proteins

Reovirus-induced acute myocarditis in mice serves as a model to investigate non-immune-mediated mechanisms of viral myocarditis. We have used primary cardiac myocyte cultures infected with a large panel of myocarditic and nonmyocarditic reassortant reoviruses to identify determinants of viral myocarditic potential. Here, we report that while both myocarditic and nonmyocarditic reoviruses kill cardiac myocytes, viral myocarditic potential correlates with viral spread through cardiac myocyte cultures and with cumulative cell death. To address the role of secreted interferon (IFN), we added anti-IFN-α/β antibody to infected cardiac myocyte cultures. Antibody benefited nonmyocarditic more than myocarditic virus spread (P < 0.001), and this benefit was associated with the reovirus M1 and L2 genes. There was no benefit for a differentiated skeletal muscle cell line culture (C2C12 cells), suggesting cell type specificity. IFN-β induction in reovirus-infected cardiac myocyte cultures correlated with viral myocarditic potential (P = 0.006) and was associated with the reovirus M1, S2, and L2 genes. Sensitivity to the antiviral effects of IFN-α/β added to cardiac myocyte cultures also correlated with viral myocarditic potential (P = 0.004) and was associated with the same reovirus genes. Several reoviruses induced IFN-β levels discordant with their myocarditic phenotypes, and for those tested, sensitivity to IFN-α/β compensated for the anomalous induction levels. Thus, the combination of induction of and sensitivity to IFN-α/β is a determinant of reovirus myocarditic potential. Finally, a nonmyocarditic reovirus induced cardiac lesions in mice depleted of IFN-α/β, demonstrating that IFN-α/β is a determinant of reovirus-induced myocarditis. This provides the first identification of reovirus genes associated with IFN induction and sensitivity and provides the first evidence that IFN-β can be a determinant of viral myocarditis and reovirus disease.