Evidence for electrogenic Na+ pumping in human atrial myocardium

The resting potential of "sodium-loaded' cardiac cells can transiently hyperpolarize to levels negative to the steady state resting potential [3,5,6]. Hyperpolarization is associated with the coupled efflux of Na+ and influx of K+ driven by an active transport process and may result from an increased K+ equilibrium potential (EK), an outward pump current or both. Using conventional microelectrode techniques, we found that Na+-loaded human atrial myocardium can also transiently hyperpolarize. Na+ loading was induced by cooling to 2 degrees to 3 degrees C. Upon rewarming to 37 degrees C in a 20 mM K+ solution, the resting potential transiently hyperpolarized to levels at least 11 mV negative to the calculated EK and 29 +/- 2 mV (mean +/- S.E.) negative to the steady state level (- 33 +/- 2 mV) recorded some 15-20 minutes later. An increase in K+ conductance induced by acetylcholine exposure [2,7,10] during the transient hyperpolarization caused a depolarization, indicating that the resting potential was indeed negative to EK. These findings cannot be explained by either conductance changes or electroneutral Na+ pumping and concomitant extracellular K+ depletion. We conclude that the Na+-loaded human atrium can generate net pump current.     

门冬氨酸钾镁治疗心力衰竭并心律失常的临床分析

目的探讨门冬氨酸钾镁治疗心力衰竭并心律失常的疗效。方法选择心力衰竭合并心律失常患者96例为治疗组，在常规综合控制心力衰竭、抗心律失常治疗的基础上，加用门冬氨酸钾镁注射液静滴；另随机抽取相应患者93例为对照组，进行疗效对比。结果治疗组用药后血清钾、镁分别为（4．50±0．31）mmol／L和（1．10±0．11）mmol／L，与用药前的（3．92±0．32）mmol／L和（0．77±0．10）mmol／L相比，差异有统计学意义（P〈O．05）。治疗前治疗组和对照组血BNP水平分别为（7560．5±56．3）pg／ml和（7620．2±54．4）pg／ml，治疗后分别为（1542．3±53．2）pg／ml和（2450．2±51．3）pg／ml，前后相比差异有统计学意义（P〈O．05）。治疗组总有效病例91例，有效率94．7％；对照组有效病例73例，有效率78．3％，两组比较差异有统计学意义（P〈0．05）。结论门冬氨酸钾镁治疗心力衰竭合并心律失常疗效较好，副作用少。     

急性心肌缺血犬心肌细胞瞬时外向钾电流和跨壁复极离散度变化致心律失常机制研究

目的:探讨急性心肌缺血对犬左室心肌楔形组织块瞬时外向钾电流(Ito)、跨壁复极离散度(TDR)变化及其与室性心律失常的关系。方法:建立冠状小动脉灌注犬左室心肌楔形组织块模型,应用浮置玻璃微电极和心电图同步记录技术,观察急性无灌流心肌缺血对内、中、外3层心肌细胞Ito、动作电位时程(APD)、TDR和心律失常的影响。结果:急性心肌缺血早期犬左室内、中、外3层心肌细胞的Ito增大,APD缩短,均以外膜心肌细胞最明显,TDR增加,诱发早期后除极、R-on-T期前收缩和室性心动过速。结论:急性心肌缺血时Ito增大,TDR增加,产生2相位折返,是多型性室性心动过速发生的重要机制。     

A single hERG mutation underlying a spectrum of acquired and congenital long QT syndrome phenotypes

The long QT syndrome (LQTS) is a multi-factorial disorder that predisposes to life-threatening arrhythmias. Both hereditary and acquired subforms have been identified. Here, we present clinical and biophysical evidence that the hERG mutation c.1039 C > T (p.Pro347Ser or P347S) is responsible for both the acquired and the congenital phenotype. In one case the genotype remained silent for years until the administration of several QT-prolonging drugs resulted into a full-blown phenotype, that was reversible upon cessation of these compounds. On the other hand the mutation was responsible for a symptomatic congenital LQTS in a Dutch family, displaying a substantial heterogeneity of the clinical symptoms. Biophysical characterization of the p.Pro347Ser potassium channels using whole-cell patch clamp experiments revealed a novel pathogenic mechanism of reciprocal changes in the inactivation kinetics combined with a dominant-negative reduction of the functional expression in the heterozygous situation, yielding a modest genetic predisposition for LQTS. Our data show that in the context of the multi-factorial aetiology underlying LQTS a modest reduction of the repolarizing power can give rise to a spectrum of phenotypes originating from one mutation. This observation increases the complexity of genotype-phenotype correlations in more lenient manifestations of the disease and underscores the difficulty of predicting the expressivity of the LQTS especially for mutations with a more subtle impact such as p.Pro347Ser.     

The change of the free energy of ATP hydrolysis during global ischemia and anoxia in the rat heart. Its possible role in the regulation of transsarcolemmal sodium and potassium gradients

The timecourse of change of the cytoplasmic free energy of ATP hydrolysis during acute global ischemia and during anoxic perfusion was determined in the isolated rat heart. The timecourse of change of transsarcolemmal Na+ and K+ gradients during anoxia, and of extracellular K+ during ischemia were measured. The free energy of ATP hydrolysis was calculated from the equilibrium of the creatinekinase reaction, taking into account the pH-dependence of the equilibrium constant, and intracellular inorganic phosphate. In control aerobic hearts the mean free energy of ATP hydrolysis was 55.2 kJ/mol. Both during ischemia and anoxia it declines biphasically. The first rapid phase terminates within 4 min into a plateau of about 46 kJ/mol. The duration of this plateau is shorter during anoxia than during ischemia. The second phase of decrease starts after 6 to 8 min during anoxia and after 15 to 20 min during ischemia. After 30 min of anoxia the free energy of ATP hydrolysis has decreased to 31 kJ/mol and after 30 min of ischemia a value of 35.5 kJ/mol is reached. The timecourses of change of measured intracellular Na+ and K during anoxia and of extracellular K+ during ischemia were also biphasic. During anoxia the loss of intracellular K+ was almost equal to the gain of intracellular Na+ at any point. Based on the assumption that the sodium pump is in thermodynamic equilibrium or near-equilibrium during anoxia and ischemia, the time-course of change of Na+ and K+ gradients during anoxia and of extracellular K+ during ischemia were calculated from the respective timecourses of change of the free energy of ATP hydrolysis. Good agreement was observed between calculated and measured changes of Na+ and K+ gradients. It is concluded that the magnitude and direction of change of transsarcolemmal ion-gradients during anoxia and ischemia may be under direct thermodynamic control of myocardial energy metabolism.     

Prediction of return of spontaneous circulation in out-of-hospital cardiac arrest with non-shockable initial rhythm using point-of-care testing: a retrospective observational study

BACKGROUND: Out-of-hospital cardiac arrest (OHCA) is a public health concern, and many studies have been conducted on return of spontaneous circulation (ROSC) and its prognostic factors. Rotational thromboelastometry (ROTEM^®), a point-of-care testing (POCT) method, has been useful for predicting ROSC in patients with OHCA, but very few studies have focused on patients with non-shockable rhythm. We examined whether the parameters of POCT could predict ROSC in patients with OHCA and accompanying non-shockable rhythm.     

The evaluation of the genotoxicity of two food preservatives: Sodium benzoate and potassium benzoate

In this study, the genotoxic effects of sodium benzoate (SB) and potassium benzoate (PB) were investigated in cultured human peripheral lymphocytes using chromosomal aberrations (CA), sister chromatid exchange (SCE), and micronuclei (MN). The level of nuclear DNA damage of SB and PB were also evaluated using the comet assay. The lymphocytes were incubated with different concentrations of SB (6.25, 12.5, 25, 50, and 100 μg/ml) and PB (62.5, 125, 250, 500, and 1000 μg/ml). A significant increase was observed in CA, SCE, and MN, in almost all treatments compared to negative controls. SB and PB significantly decreased the mitotic index (MI) in all the treatments, compared to the negative controls. However, neither of the additives affected the replication index (RI). Although SB significantly increased DNA damage, PB did not cause a significant increase in DNA damage. The present results indicate that SB and PB are clastogenic, mutagenic and cytotoxic to human lymphocytes in vitro.     

Purification and characterization of Ts15, the first member of a new α-KTX subfamily from the venom of the Brazilian scorpion Tityus serrulatus

Voltage-gated potassium channel toxins (KTxs) are basic short chain peptides comprising 23-43 amino acid residues that can be cross-linked by 3 or 4 disulfide bridges. KTxs are classified into four large families: α-, β-, γ- and κ-KTx. These peptides display varying selectivity and affinity for K_v channel subtypes. In this work, a novel toxin from the Tityus serrulatus venom was isolated, characterized and submitted to a wide electrophysiological screening on 5 different subtypes of Na_V channels (Na_V1.4; Na_V1.5; Na_V1.6; Na_V1.8 and DmNa_V1) and 12 different subtypes of K_V channels (K_V1.1 - K_V1.6; K_V2.1; K_V3.1; K_V4.2; K_V4.3; Shaker IR and ERG). This novel peptide, named Ts15, has 36 amino acids, is cross-linked by 3 disulfide bridges, has a molecular mass of 3956 Da and pI around 9. Electrophysiological experiments using patch clamp and the two-electrode voltage clamp techniques show that Ts15 preferentially blocks K_V1.2 and K_V1.3 channels with an IC₅₀ value of 196 ± 25 and 508 ± 67 nM, respectively. No effect on Na_V channels was observed, at all tested concentrations. Since Ts15 shows low amino acid identity with other known KTxs, it was considered a bona fide novel type of scorpion toxin. Ts15 is the unique member of the new α-Ktx21 subfamily and therefore was classified as α-Ktx21.1.     

浙江省居民膳食钠钾摄入水平

目的分析浙江省居民膳食钠、钾摄入水平。方法运用3d24h回顾法和调味品称重法相结合,对浙江省11个地市共9 798名调查对象进行膳食调查,将食物消费数据结合食物钠、钾含量数据,分析膳食中钠和钾的摄入水平。数据采用SPSS16.0进行统计分析。结果 2～3岁、4～6岁、7～10岁、11～13岁、14～17岁、18～44岁、45～59岁、60岁及以上人群,每日膳食钠摄入中位数(第25百分位数～75百分位数)为4 324(3 258～6 184)mg、4 439(3 135～5 976)mg、4 686(3 345～6 540)mg、4 875(3 518～6 665)mg、4 754(3 452～6 453)mg、4 924(3 504～6 666)mg、5 121(3 776～6 983)mg、5 207(3664～7228)mg;2～3岁、4～13岁、14～17岁、18～44岁、45～59岁、60岁及以上人群,每日膳食钾摄入中位数(25百分位数～75百分位数)分别为779(571～1106)mg、953(686～1331)mg、1137(855～1566)mg、1354(986～1795)mg、1528(1132～1953)mg、1644(1269～2159)mg、1660(1289～2226)mg、1571(1162～2155)mg。相比城市居民,农村居民摄入更多的钠和更少的钾。相比内陆地区,沿海地区居民摄入更多的钠,差异具有统计学意义。约82.0%的膳食钠来源于食盐、酱油;蔬菜和水果提供了膳食钾中的25%,谷类提供了27.8%,豆类提供12.2%的膳食钾。结论浙江省居民膳食钠摄入过量,膳食钾摄入不足。应该进行营养干预,以达到人群膳食钠、钾摄入平衡。     

阻断BDNF-TrkB通路后运动训练对脊髓损伤大鼠痉挛状态及KCC2表达的影响

目的 探讨阻断脑源性神经营养因子（BDNF）-酪氨酸激酶受体B（TrkB）通路后运动训练对脊髓损伤（SCI）大鼠痉挛状态及钾-氯协同转运蛋白2（KCC2）表达的影响。 方法 将40只雌性 SD大鼠按随机数字表法分为假手术组（Sham组）、SCI+磷酸盐缓冲液组（SCI/PBS组）、SCI-运动训练+PBS组（SCI-TT/PBS组）、SCI/TrkB-IgG组和SCI-TT/TrkB-IgG组。于SCI前1周对所有大鼠进行鞘内置管,置管1周后制作T10不完全SCI大鼠模型,Sham组仅暴露脊髓。于SCI制模术后第 7天,使用TrkB-IgG阻断SCI/TrkB-IgG和SCI-TT/TrkB-IgG组的BDNF-TrkB信号通路,其余三组使用PBS进行对照。SCI后第8天,SCI-TT/PBS组和 SCI-TT/TrkB-IgG组进行4周的减重平板训练。使用Asworth评定法和H反射（H-max/M-max比值）评估大鼠后肢的痉挛状态。实验结束后采用 Western Blot和免疫组化技术检测各组大鼠损伤远段脊髓 KCC2的表达情况。 结果 SCI后1～5周,4组SCI大鼠的Ashworth痉挛分级均较Sham组增加。SCI后3～5周,SCI-TT/PBS组Ashworth痉挛分级明显小于SCI/PBS组和SCI/TrkB-IgG组（P＜0.05）;SCI后第5周,SCI-TT/PBS组Ashworth痉挛分级小于SCI-TT/TrkB-IgG组（P＜0.05）;SCI后1～5周,Sham组H-max/M-max比值保持不变,均低于4组SCI大鼠（P＜0.05）。SCI后第1周和第2周,4组SCI大鼠H-max/M-max比值差异无统计学意义（P＞0.05）。SCI后3～5周,SCI-TT/PBS组H-max/M-max比值明显低于SCI/PBS组、SCI/TrkB-IgG组和SCI-TT/TrkB-IgG组（P＜0.05）。SCI后4～5周,SCI-TT/TrkB-IgG组H-max/M-max比值明显低于SCI/TrkB-IgG组（P＜0.05）。KCC2免疫组化及Western Blot结果显示,SCI 5周后,4组SCI大鼠的损伤远端脊髓前角KCC2的表达量较Sham组明显减少（P＜0.05）。运动训练可明显增加SCI-TT/PBS组KCC2的表达量,其免疫强度和相对光密度值均高于SCI/PBS组、SCI/TrkB-IgG组和SCI-TT/TrkB-IgG组（P＜0.05）。而SCI/TrkB-IgG组与SCI-TT/TrkB-IgG组差异无统计学意义（P＞0.05）。 结论 减重平板训练可通过BDNF-TrkB信号通路改善 SCI大鼠的痉挛状态并促进损伤远端脊髓内KCC2的表达。