β-Adrenergic and muscarinic receptor mRNA accumulation in the sinoatrial node area of adult and senescent rat hearts

The sinoatrial (SA) node is the cardiac pacemaker and changes in its adrenergic-muscarinic phenotype have been postulated as a determinant of age-associated modifications in heart rate variability. To address this question, right atria were microdissected, the SA node area was identified by acetylcholinesterase staining, and, using a RT-PCR method, the accumulation of mRNA molecules encoding β₁- and β₂-adrenergic (β₁- and β₂-AR) and muscarinic (M₂-R) receptor was quantified to define the proportion between β-AR and M₂-R mRNAs within the sinoatrial area of adult (3 months) and senescent (24 months) individual rat hearts. In adult hearts, the highest M₂-R/β-AR mRNA ratio was observed within the sinoatrial area compared with adjacent atrial myocardium, while in the senescent hearts, no difference was observed between sinoatrial and adjacent areas. This change was specific of the sinoatrial area since adult and senescent whole atrial or ventricular myocardium did not differ in their M₂-R/β-AR mRNA ratio, and was associated with a fragmentation of acetylcholinesterase staining of the senescent SA node. Quantitative changes in the expression of genes encoding proteins involved in heart rate regulation specifically affect the sinoatrial area of the senescent heart.     

Computer modelling of the sinoatrial node

Over the past decades patch-clamp experiments have provided us with detailed information on the different types of ion channels that are present in the cardiac cell membrane. Sophisticated cardiac cell models based on these data can help us understand how the different types of ion channels act together to produce the cardiac action potential. In the field of biological pacemaker engineering, such models provide important instruments for the assessment of the functional implications of changes in density of specific ion channels aimed at producing stable pacemaker activity. In this review, an overview is given of the progress made in cardiac cell modelling, with particular emphasis on the development of sinoatrial (SA) nodal cell models. Also, attention is given to the increasing number of publicly available tools for non-experts in computer modelling to run cardiac cell models.     

家猫窦房结的光镜观察

目的探讨猫心窦房结的形态特征。方法①取新鲜猫心窦房结组织,常规石蜡包埋切片,苏木精-伊红和Masson染色,光学显微镜观察记录;②利用透射电镜技术观察猫窦房结的亚微结构。结果猫窦房结位于界沟的腔静脉窦侧,心内外膜之间;上端距腔耳角3.1mm,末端最长延伸到下腔静脉口;主要由起搏细胞和移行细胞组成,起搏细胞分为亮细胞和暗细胞。移行细胞的形态介于起搏细胞和普通心肌细胞之间。结细胞之间存在较多的胶原纤维。窦房结动脉不位于结的中央。结论猫窦房结位置相对较低,结组织较为典型,可作为窦房结实验的典型动物使用。     

The artery of the sinuatrial node: anatomic considerations based on 45 injection-dissections of the heart

Summary The origin, course and mode of termination of the artery of the sinuatrial node was studied in 45 anatomic specimens by injection-dissection. It was solitary in 88.89% of the cases and double in 11.11%. It arose from the right coronary a. in 64.45% of cases, from the left coronary a. in 24.44%, and from both in 11.11%. The side of origin was not significantly influenced by the coronary dominance. When it arose from the right coronary a., the course of the sinuatrial a. varied greatly with its site of origin from the coronary vessel, either from an atrial a. or from one of its collateral branches, and also depended on its relations with the interatrial septum. When it arose from the left coronary a., its course was relatively uniform, except for arteries arising from the inferior atrial aa., which characteristically involve the posterior wall of the left atrium. Three modes of termination were found: precaval, retrocaval, and in a pericaval arterial circle. These observations made it possible to understand the possible origin of disorders of rhythm observed following disturbance of the arterial supply to the sinuatrial node during certain stages of cardiac surgery, particularly during atriotomies and the surgical correction of certain valvular disorders and congenital malformations, which expose the a. of the sinuatrial node.

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L'artère du nud sinu-atrial : considérations anatomiques à propos de 45 injections - dissections du cur

Résumé Sur 45 pièces anatomiques, les auteurs ont étudié, par la méthode d'injection-dissection, l'origine, le trajet et le mode de terminaison de l'a. du nud sinu-atrial. Unique dans 88,89 % des cas, double dans 11,11 % des cas, elle naissait de l'a. coronaire droite dans 64,45 % des cas, de l'a. coronaire gauche dans 24,44 % des cas et des deux dans 11,11 % des cas. Ce mode d'origine n'a pas été influencé de manière significative par la dominance coronarienne. En cas d'origine droite, le trajet de l'artère a été très variable selon le niveau de naissance sur l'a. coronaire, selon qu'il s'agissait d'une a. atriale ou d'une de ses branches collatérales et selon ses rapports avec le septum interatrial. En cas d'origine gauche, le trajet est relativement stéréotypé à l'exception des artères naissant des aa. atriales inférieures qui ont la particularité d'intéresser la paroi postérieure de l'atrium gauche. Les trois modes de terminaison en précave, en rétrocave et en cercle artériel ont été rencontré. Ces observations anatomiques ont permis aux auteurs de comprendre l'origine possible des troubles du rythme observés à la suite d'une perturbation de l'apport artériel au nud sinu-atrial au cours de certains temps de la chirurgie cardiaque, en particulier au cours des atriotomies et de la correction chirurgicale de certaines valvulopathies et malformations congénitales qui exposent l'a. du nud sinu-atrial.

     

Cardiac responses to exercise in the dog before and after destruction of the sinoatrial node

Summary Chronotropic and dromotropic responses to treadmill exercise were compared in conscious dogs prior to and following excision of the sinoatrial node (SAN). The initial junctional rhythm accompanying removal of the SAN region was replaced within hours to days by subsidiary atrial pacemaker (SAP) foci located in the inferior right atrium along the sulcus terminalis. With SAN intact, cardiac acceleration was immediate at onset of exercise and the tachycardia was directly proportional to work intensity. Atrioventricular (AV) conduction concurrently accelerated during exercise as manifest by shortening in P-R and atrioventricular (A-V) intervals. Following SAN excision, subsidiary atrial pacemaker foci likewise demonstrated prompt tachycardias during exercise, although heart rate was significantly reduced at rest and during steady state exercise. In the SAP state, tachycardia during exercise was related to work intensity and was mediated by changes in cardiac autonomic nerve activity. Combined propranolol-atropine blockade increased heart rate at rest in the SAP state, and significantly attenuated the tachycardia accompanying treadmill exercise. Following SAN excision the P-R (A-V) interval was significantly reduced in the resting animal. In response to exercise, AV conduction time decreased in the SAP state, though the absolute levels during steady state exercise were not significantly different from prior control runs with SAN intact. Blood pressure response to exercise was similar during both SAN and SAP states. We conclude that following an initial unstable period, SAP foci maintain adequate heart rate increases in response to dynamic exercise, primarily mediated via autonomic nerve regulation. Supported by NIH Grants HL 27595, HL 27664, HL 28205, and HL 32392     

Comparative iTRAQ analysis of protein abundance in the human sinoatrial node and working cardiomyocytes

Our objective was to assess the changes in protein abundance in the human sinoatrial node (SAN) compared with working cardiomyocytes to identify SAN‐specific protein signatures. Four pairs of samples (the SAN and working cardiomyocytes) were obtained postmortem from four human donors with no evidence of cardiovascular disease. We performed protein identification and quantitation using two‐dimensional chromatography‐tandem mass spectrometry with isobaric peptide labeling (iTRAQ). We identified 451 different proteins expressed in both the SAN and working cardiomyocytes, 166 of which were differentially regulated (110 were upregulated in the SAN and 56 in the working cardiomyocytes). We identified sarcomere structural proteins in both tissues, although they were differently distributed among the tested samples. For example, myosin light chain 4, myosin regulatory light chain 2‐atrial isoform, and tropomyosin alpha‐3 chain levels were twofold higher in the SAN than in working cardiomyocytes, and myosin light chain 3 and myosin regulatory light chain 2‐ventricular/cardiac muscle isoform levels were twofold higher in the ventricle tissue than in SAN. We identified many mitochondrial oxidative phosphorylation, β‐oxidation, and tricarboxylic acid cycle proteins that were predominantly associated with working cardiomyocytes tissue. We detected upregulation of the fatty acid omega activation pathway proteins in the SAN samples. Some proteins specific for smooth muscle tissue were highly upregulated in the SAN (e.g. transgelin), which indicates that the SAN tissue might act as the bridge between the working myocardium and the smooth muscle. Our results show possible implementation of proteomic strategies to identify in‐depth functional differences between various heart sub‐structures.     

非体外循环下冠状动脉旁路移植围术期血浆脑钠肽释放及其相关性研究

背景：B型脑钠肽已成为心血管疾病诊断重要的血清标志物,作为心血管疾病危险因素分层的重要因子。 目的：分析冠状动脉旁路移植前后B型脑钠肽与各项血流动力学参数的关系。 方法：选择30例冠心病行冠脉旁路移植患者,分为左室射血分数≥ 50%心功能正常患者13例;左室射血分数< 50%心功能不全患者17例。观察患者移植前1 d、移植后7 h、移植后1,3,5,7 d血浆B型脑钠肽水平变化趋势,分析移植前后B型脑钠肽与心功能各项指标的相关关系。 结果与结论：左室射血分数≥ 50%组患者冠脉旁路移植前后血浆B型脑钠肽水平显著低于左室射血分数< 50%组;组内比较移植后血浆B型脑钠肽水平均显著高于移植前(P < 0.05或P < 0.001)。患者冠脉旁路移植前B型脑钠肽水平与纽约心脏病协会心功能分级、左房内径、左室内径呈正相关(r=0.61;r=0．34;r=0．67);与左室射血分数、心排血量呈负相关(r=-0.75;r=-0.70)。患者移植后B型脑钠肽峰值浓度与出院前纽约心脏病协会心功能分级、超声心动图左室舒张末期内径、肺动脉压力呈正相关(r=0.72;r=0.70;r=0.45)。结果说明冠心病患者冠脉旁路移植前血浆B型脑钠肽质量浓度与左心室射血分数及左心室舒张末期内径有很好的相关性,能准确反映冠脉旁路移植前后的心功能状态。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

Phase response characteristics of sinoatrial node cells

In this work, the dynamic response of the sinoatrial node (SAN), the natural pacemaker of the heart, to short external stimuli is investigated using the Zhang et al. model. The model equations are solved twice for the central cell and for the peripheral cell. A short current pulse is applied to reset the spontaneous rhythmic activity of the single sinoatrial node cell. Depending on the stimulus timing either a delay or an advance in the occurrence of next action potential is produced. This resetting behavior is quantified in terms of phase transition curves (PTCs) for short electrical current pulses of varying amplitude which span the whole period. For low stimulus amplitudes the transition from advance to delay is smooth, while at higher amplitudes abrupt changes and discontinuities are observed in PTCs. Such discontinuities reveal critical stimuli, the application of which can result in annihilation of activity in central SAN cells. The detailed analysis of the ionic mechanisms involved in its resetting behavior of sinoatrial node cell models provides new insight into the dynamics and physiology of excitation of the sinoatrial node of the heart.     

人窦房结胶原纤维网架的构筑

目的：观察人窦房结胶原纤维网架的构筑及其与窦房结中央动脉的关系。方法：用NaOH消蚀法扫描电镜观察成人窦房结。结果：人窦房结中央动脉管壁的纤维网架分为内膜、中膜和外膜3层;在窦房结中央动脉周围,形成厚约50～80μm的致密的动脉周围层;再向外是中央层,窦房结实质细胞就位于其胶原纤维隔围成的直径约8～16μm的孔洞中;中央层与普通心肌胶原纤维网架间的界限明显。结论：人窦房结胶原纤维网架的构筑,有利于消除中央动脉博动的影响,并为窦房结实质细胞构筑一个相对稳定的微环境。     

窦房结的外科解剖

在95例成人与30例儿童心脏上,用解剖显微镜观察、解剖和测量了窦房结。在成人,此结多数可以用色苍白,质地硬.有动脉穿入等特点,在界沟上部予以确认,儿童则不易辨识。描述了右心耳嵴顶端的变异和界沟上部的切迹,并提出了窦房结三角以确认此结。对结的外表标志及其肌肉连系结合外科和功能进行了讨论。     

右冠状动脉急性缺血/再灌注时窦房结细胞凋亡与iNOS蛋白的表达

目的 观察在体兔右冠状动脉急性缺血/再灌注(L/R)时窦房结细胞凋亡与诱导型一氧化氮合酶(iNOS)蛋白表达的关系。方法 在体兔右冠状动脉根部结扎或放松制作窦房结缺血/再灌注模型,健康成年新西兰兔70只分7组:假手术对照组、I2h组、I2hR2h组、I2h+NS(生理盐水)组、I2h+SMT(iNOS抑制剂Smethylisothiourea,SMT)组、I2hR2h+NS组和I2hR2h+SMT组。采用末端标记TUNEL法、SP免疫组化法结合彩色图像分析技术,检测窦房结细胞凋亡指数(AI)及iNOS蛋白表达的积分光密度(A)值。结果 ①I2hR2h组AI及iNOS A值明显高于12h组(P<0.01);②应用iNOS抑制剂后,I2h+SMT组、I2hR2h+SMT组AI及iNOS A值均明显低于I2h组和I2hR2h。组(P<0.05或P<0.01)。结论 缺血诱导窦房结细胞凋亡,再灌注加重细胞凋亡和增加iNOS表达,且细胞凋亡指数与iNOS表达变化相一致。提示iNOS生成增多可能与缺血再灌注窦房结细胞凋亡密切相关。     

Variations of the superficial brachial artery in Korean cadavers

The superficial brachial artery (SBA), a branch of the axillary artery, is one of the most common arterial variations in this area. While it is more vulnerable to accidental arterial injection or injury, it could be useful for the nourishment of a medial arm skin free flap. To analyze the relationship between the SBA of axillary origin and segmental variation of the axillary artery, we dissected 304 arms of Korean cadavers. We found an SBA of axillary origin in 12.2% of cadaveric arms. Unilateral occurrence was detected in 16 cadavers and bilateral in 10. SBAs gave rise to radial and ulnar arteries in the cubital fossa (8.9%), continued in the forearm as the radial artery (2.3%), or ended in the upper arm (1.0%). The SBA ended as ulnar artery was not found in any of the cadavers. The bifurcation of the SBA into the radial and ulnar arteries, presence of an SBA that ends in the upper arm, and the lack of continuation as the ulnar artery are characteristics of SBAs in Korean cadavers.     

The surgical anatomy of the sinoatrial node

Summary The sinoatrial nodes (SAN) were observed, dissected, and measured on 95 adults and 30 child hearts under a dissection microscope. The majority of the SANs in adults are characterized by their pale color, firm consistency, and the location in relation to the penetration of the SAN artery, and they can be located in the superior part of the terminal sulcus. The SANs in children, however, are not easily discerned. The variation of the apex of the right auricular crest and the notch in the superior part of the terminal sulcus have been described, and the present authors suggested that the trigone of the SAN could be used as an important landmark to identify the SAN. The surface features on the SAN, its relationship to the surrounding, myocardium and its surgical significance during operation are further discussed.

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Anatomie chirurgicale du nud sinu-atrial

Résumé Le nud sinu-atrial (NSA) a été observé, disséqué et mesuré sur les curs de 95 adultes et 30 enfants lors de dissections sous microscope. La majorité des NSA est caractérisée chez l'adulte par une coloration pâle, une consistance ferme, et une situation en regard du lieu de pénétration de l'artère du nud sinu-atrial, à la partie craniale du sillon terminal. Chez l'enfant, le NSA est toutefois difficile à discerner. Les variations de l'apex de la crête de l'auricule droite et l'incisure à la partie craniale du sillon terminal ont été décrits, et les auteurs suggèrent que le triangle du NSA puisse être considéré comme un important repère pour identifier le NSA. Les caractéristiques de la surface du NSA, ses relations avec le myocarde avoisinant et sa valeur chirurgicale peropératoire sont ensuite discutées.

     

Blockade of the delayed rectifier K+ currents, I Kr, in rabbit sinoatrial node cells by external divalent cations

We investigated the actions of various divalent cations on the delayed rectifier K⁺ currents (I _Kr) in rabbit sinoatrial node cells using the whole-cell voltage-clamp technique in isotonic K⁺ solutions. External divalent cations decreased the amplitude of currents, accelerated the time course of deactivation and shifted the activation to positive potentials in a dose-dependent manner. The concentrations for half-maximum inhibition of the steady-state currents (K _M) obtained at 0 mV were 0.63, 1.36, 1.65 and 2.16 mM for Ni²⁺, Co²⁺, Mn²⁺ and Ba²⁺, respectively. The effect was voltage dependent (K _M decreased e-fold for 12.2–16.8 mV hyperpolarization), but the dependence did not vary significantly among different cations. Acceleration of the time course of current deactivation by the increase of divalent cation concentration was well fitted by the voltage-dependent block model, and the binding rate constant (k ₁) was obtained. The binding rates for the ions took the following order: Ni²⁺ >Co²⁺ >Mn²⁺ >Ba²⁺. The degree of the shift of activation occurred in the same order: Ni²⁺ >Co²⁺ >Mn²⁺ >Ba²⁺. From these results, we conclude that I _Kr channels are non-selectively blocked by most divalent cations from the external side and that the binding site is located deep inside the channel, resulting in a steep voltage dependence of the blockade. Received: 26 January 1999 / Received after revision: 16 March 1999 / Accepted: 18 March 1999     

Monovalent cation conductance of the sustained inward current in rabbit sinoatrial node cells

 Under the whole cell clamp, superfusion of the rabbit sinoatrial node cells with a Na⁺-free solution suppressed the sustained inward current (I_st), and the L-type Ca²⁺ current (I_Ca,L) could be recorded on depolarization less negative than –40 mV from the holding potential of –80 mV. On the other hand, replacement of Ca²⁺ with Mg²⁺ in the external solution suppressed inward-going I_Ca,L and isolated I_st. Under this condition, I_st measured as a nicardipine-sensitive current showed an activation threshold between –60 and –70 mV. The conductance sequence of I_st for monovalent ions was determined as Na⁺ > Li⁺ >> K⁺ @ Cs⁺ by replacing the external Na⁺ with these alkali metal ions. The contribution of I_st to the diastolic depolarization is discussed. Received: 12 June 1996 / Received after revision: 31 July 1996 / Accepted: 7 August 1996     

Inward current of the rabbit sinoatrial node cell

Summary Inward currents of the rabbit sinoatrial node cell were examined in voltage-clamp experiments using the two-microelectrode technique. A fast and slow inward current could be separated from each other. The slow inward current was blocked by Mn and D 600, but it was insensitive to TTX. On the contrary, the fast inward current was blocked by TTX, but not by Mn and D 600. Both the fast and slow inward current disappeared on Na removal.The fast inward current system was fully inactivated by holding the membrane potential positive to –40 to –50 mV, while the slow inward current system was recorded with the holding potential up to –20 mV. The voltage dependence of the inactivation of the 2 inward current systems and their dependence on [Na]₀ suggests that the rising phase of the spontaneous action potential in the S-A node cell is produced mainly by Na current through the slow inward current system.     

心第3冠状动脉的解剖学

目的:研究心第3冠状动脉的大体解剖学数据,为临床诊治相关疾病提供依据。方法:共收集了118个福尔马林固定的心,观测心第3冠状动脉数量、来源、分布范围、营养区域和长度及管径等解剖学数据。结果:第3冠状动脉出现率为28.8%,其中单支出现率为26.3%,双支出现率为2.5%。它通常分布于动脉圆锥、右心室前壁、室间隔及心尖中的1个或多个位置,也有些少见情况:第3冠状动脉比右冠状动脉大并结束于心尖;第3冠状动脉比右冠状动脉小且结束于心尖;心肌桥覆盖较大的第3冠状动脉。结论:心存在第3冠状动脉情况较多,它与左冠状动脉前降支吻合且分布于心尖和室间隔。因此第3冠状动脉是在疾病诊疗期间需要着重考虑的一个因素。     

Conductance of the slow inward channel in the rabbit sinoatrial node

The elementary conductance of the slow inward current channel in the rabbit sinoatrial node was measured by analysis of the current fluctuations. The preparations were voltage-clamped to –30 mV, where d and f of the slow inward current (I_si) intersect. In the presence of Ba, which increases I_si and decreases outward currents, a small steadystate component of I_si could be detected.The fluctuations of the current in 10 mM Ba were smaller due to the block of the outward channels. They were further reduced after the inhibition of I_si by the Ca channel blocker D600. The spectral power density distribution of the current fluctuations originating from I_si could be fitted at frequencies <30 Hz with a single Lorentzian which was attributed to the inactivation process. The corner frequency was 5.28 ±1.16 Hz (n=10), corresponding to an average open time of the single channel of about 30 msec at –30mV. The single channel conductance was determined to 6.50±3.15 pS (S.D.,n=10).This work was supported by the Deutsche Forschungsgemeinschaft SFB 38, Membranforschung, project G