高果糖诱导IR大鼠模型血清脂质代谢的改变及意义

目的: 评估高果糖膳食对机体胰岛素敏感性及血清脂质代谢的影响及意义.方法:以高果糖膳食(果糖占总热量34.5%)诱导并经钳夹技术证实建立胰岛素抵抗(IR)大鼠模型,生化比色法测定血清游离脂肪酸(FFA),生化酶法测定血清甘油三酯(TG)及总胆固醇(TC).结果:高果糖膳食喂养4周后,实验组大鼠葡萄糖输注率由(11.5±0.6)mg/kg·min-1下降至(6.6±0.4)mg/kg·min-1(P<0.01);血清FFA由(0.45±0.09)mmol/L增至(0.78±0.19)mmol/L(P<0.01);TG由(0.54±0.10)mmol/L增至(0.96±0.22)mmol/L(P<0.01);TC由(1.96±0.32)mmol/L增至(2.42±0.21)mmol/L(P<0.01).结论:高果糖膳食可导致机体严重IR,是建立IR大鼠模型的有效手段;该模型同时伴有血清脂代谢各相关指标的明显异常,血脂的变化既是IR的结果,也是IR向纵深发展的原因和必要条件.     

微波照射对小鼠海马细胞膜ATPase活性和离子通道的影响

目的从电生理、酶学角度探讨微波照射对海马细胞的影响机理。方法用 2 4 5 0MHz连续波照射理疗机为照射源 ,以小白鼠为对象 ,观察微波照射强度为 1 0mW /cm2 时小鼠海马细胞膜Na+,K+ AT Pase、Ca2 +,Mg2 + ATPase活性、电压门控型Na+、K+、Ca2 +通道的变化情况 ,分别用组织化学染色法和膜片钳方法测定ATPase活性和离子通道功能。结果 1 )照射组海马Na+,K+ ATPase活性与对照组无显著差别 ,Ca2 +,Mg2 + ATPase活性比对照组显著降低 (P <0 .0 5 ) ;2 )照射组静息电位未发生显著变化 ,电压门控型Na+、K+、Ca2 +电流的诱导发生率显著地低于对照组 ,Na+电流峰值所在膜电位向去极化方向偏移 ,Na+电流衰减速率减慢 ,A电流的发生率显著低于对照。结论 2 4 5 0MHz微波照射小鼠 ,在 1 0mW /cm2 时 ,细胞的生存不会受影响 ,但海马细胞膜Ca2 +,Mg2 + ATPase活性受到抑制 ,电压门控型Na+、K+、Ca2 +离子通道受到损害 ,有可能影响学习记忆功能     

WHERE ARE THE GATES IN GAP JUNCTION CHANNELS?

1. In the formation and function of gap junction channels two types of gates ought to be discriminated: the docking gate and the channel gates proper. The docking gate is involved in the transformation of a closed hemichannel to a patent gap junction channel. By definition the trigger mechanism for this gate and maybe even the gate itself is contained within the extracellular loops of the gap junction proteins, the connexins. The channel gates proper determine the open and closed states of the complete gap junction channels. 2. Probing the docking gate by mutagenesis of connexins and by synthetic peptides indicates that this gate is the consequence of complex interactions between a large fraction of the amino acids comprising the extracellular loops. Probably both inter- and intra-molecular interactions are involved, and disulfide exchange may be entailed in the stabilization of the open and closed states. 3. Of the various effectors on the channel gate(s) the voltage effects have obtained the most scrutiny to date. The response of gap junction channels and hemichannels is diverse, the various channels respond differently to transjunctional and membrane potential. No equivalent to the S4 segment representing the voltage sensor in other voltage dependent ion channels is present in the connexin sequences, instead mutations in various segments of connexins have been reported to affect the voltage dependence of gap junction channels. To understand the complexity of voltage effects on gap junction channels, non-connexin peptides may need to be considered as voltage sensors or as modifiers thereof.     

体表电位标测微机系统(Ⅰ型)

本系统的107个电极中,103个分布于胸、背部,1个为参考电极,1个为V_3,其余用于肢导。本系统除能绘出2、4、8ms任意间隔的103通道同步的体表等电位图,常规12导联和V_(7 9)心电图,胸、背部位的心电图外,还可记录R峰值等电位图,∑R,Q波等电位图,nQ30、40,极大、极小轨迹图等。     

A Critical Period of Ventricular Fibrillation More Susceptible to Defibrillation: Real-Time Waveform Analysis Using a Single ECG Lead

Previous studies have suggested that variations in the underlying ventricular fibrillation (VF) waveform may be one of the factors responsible for the probabilistic nature of defibrillation. The heart appeared to be more susceptible to defibrillation at higher absolute VF voltages (AVFV). This study investigated in an open-chest canine model (n = 8), a newly developed system that analyzed the VF waveform in real-time, instantaneously determined the time to shock, and immediately delivered a fixed low energy DC shock. A two parameter tracking technique using a running long-term and short-term AVFV average was devised to automatically identify a high voltage peak area of the VF waveform, which has been hypothesized to represent a critical period susceptible to defibrillation. Using a DC shock estimated at the 50% success level, the performance using this technique in 58 defibrillation trials was compared to the performance of the conventional method of shocking at a fixed time (random shock method) in 62 trials. Patch size, electrode location, and discharge voltage were kept constant while VF duration, transmyocardial resistance (TMR), energy delivered, and AVFV at the point of shock were measured. Shock energy and current, TMR, and VF duration were similar with both shock methods. A significantly higher AVFV was observed for trials performed with the peak shock method (0.66 ± 0.02 mV) as compared to trials performed with the random shock method (0.25 ± 0.09 mV) (P < 0.003). Using lead II as the only sensing lead, the success rate was increased in 6 of 8 dogs (75%) with the new method. One animal showed identical performance, and one animal a worse performance. The overall increase in success rate was 24% using a single ECG lead (range 0%-100%; P < 0.04). Our data document that using this algorithm a period of high VF voltage can be detected in realtime. The improved success in the majority of animals supports the hypothesis that a critical period susceptible to defibrillation exists during VF. However, the high AVFV detected using a single ECG lead did not translate to an improved success rate in all animals. This suggests that other factors in addition to the VF voltage measured on a single lead of the ECG are important in characterizing this critical period.     

Ion conductances of isolated cortical collecting duct cells

The study of ion conductances in the intact cortical collecting duct (CCD) with the patch-clamp method is rather difficult. An optimized method to isolate CCD cells from rat kidneys using an in vivo followed by an in vitro enzyme digestion is described. Individual CCD segments were collected after this digestion and incubated in EGTA-buffered medium. This procedure resulted in single cells or cell clusters. These freshly isolated CCD cells were studied with different modifications of the patch-clamp method. Membrane voltages measured in the cell-attached-nystatin configuration were –74 ±1mV (n=13) and –68±3 mV (n=22) in cells isolated from normal and mineralocorticoid-treated rats respectively. These values and those measured with the nystatin-perforated slow-whole-cell configuration (–79 ±1mV, n=23) are comparable to those measured in principal cells of isolated CCD segments. The cells hyperpolarized after the addition of amiloride and depolarized with the addition of adiuretin to the bath. The amiloride effect was enhanced when cells were isolated from deoxycorticosterone-acetate-treated rats. The cells were strongly depolarized upon elevation of the extracellular K⁺-concentration and did not demonstrate a measurable Cl^– conductance. A large-conductance K⁺ channel (174 pS, n=5, cell-attached, 145 mmol/l K⁺ in the pipette; 140 pS, n=12, cell-free, 3.6 mmol/l K⁺ in the bath) was seen. It had a very low activity on the cell, but a high open probability when excised into a solution with 1 mmol/l Ca²⁺ on the cytosolic side. More often a small-conductance K⁺ channel (36–52 pS, n=19, cell-attached; 30 pS, n=5, cell-free) with a high open probability was found on the cell. These freshly isolated cells seem to be a powerful preparation to study the properties and regulation of ion conductances of rat CCD with several electrophysiological methods. These freshly isolated CCD cells maintain the conductance properties known from principal cells of the intact CCD.     

内皮素-1对高血压病患者肠系膜动脉平滑肌细胞钙激活钾通道活性的影响

目的　探讨内皮素 1(ET1)对高血压病患者血管平滑肌细胞KCa通道活性的影响。方法　选择高血压病患者 18例 ,血压正常者 17例 ,两组患者均于腹部手术时取肠系膜动脉小分支用酶消化法获得单个血管平滑肌细胞。以膜片钳技术检测KCa通道的活性 ,记录不同钳制电压下单通道电流的平均开放时间 (To)、平均关闭时间 (Tc)、平均开放概率 (Po)、电流幅值 (Am) ,并绘制成电流 电压关系曲线。再分别加入Ca2 + (10 -8、10 -7、10 -6mol/L)、ET1(2× 10 9mol/L、4×10 9mol/L、6× 10 9mol/L、8× 10 9mol/L)后检测To、Tc、Po、Am等参数变化。结果　①高血压病患者KCa通道活性变化 :于细胞内面向外膜片下 ,在对称性高钾液中 ,高血压病组KCa通道平均开放概率增加 ,关闭时间延长、开放时间缩短。在浴液中分别加入Ca2 + 后 ,两组KCa通道均被明显激活 ,但血压正常组Po的增加显著高于高血压病组 (P <0 .0 0 1)。②ET1对高血压病患者KCa通道活性的影响 :血压正常者在内面向外式膜片下 ,Po、Tc均先增加后降低 ,显示低浓度时兴奋、高浓度时抑制 ,然而高血压病患者肠系膜血管平滑肌KCa通道对ET1则缺乏反应。结论　高血压病患者肠系膜动脉平滑肌细胞KCa通道活性明显高于血压正常者 ,但对Ca2 + 的敏感性降低。ET1对高血压病人KC     

The short insulin tolerance test for determination of insulin sensitivity: a comparison with the euglycaemic clamp.

The glucose clamp technique is currently regarded as the standard test for measuring insulin sensitivity against which other methods are compared but is unsuitable for routine screening of patients outside a hospital base. There is thus a need for a simpler test to measure insulin sensitivity. We have therefore compared the glucose disappearance rate KITT in the first 15 min of the insulin tolerance test (ITT) with the M and M/I values derived from the standard euglycaemic clamp in nine normal subjects and eight subjects with Type 2 (non-insulin dependent) diabetes mellitus and coexisting obesity. All subjects underwent the ITT and euglycaemic clamp in random order. Nine subjects later had a repeat ITT to determine the reproducibility of the test. In the ITT, 0.1 U kg-1 body weight, human Actrapid insulin was given as an IV bolus and simultaneous arterialized and venous blood samples were obtained every minute for 15 min. The first order rate constant for the disappearance of glucose KITT over the period 3-15 min was taken as a measure of insulin sensitivity. The euglycaemic clamp was performed with an insulin infusion of 50 mU kg-1 h-1 for 120 min and a variable rate glucose infusion to maintain blood glucose concentration at 0.5 mmol l-1 below fasting level to minimize the effect of endogenous insulin secretion. The ratio of the mean rate of glucose infused (M, mumol kg-1 min-1) to the plasma insulin over the last 30 min of the clamp was taken as a measure of tissue sensitivity to insulin (M/I) assuming endogenous glucose output was suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)     

SOMATOM CT高压熔断丝炸裂故障分析

简要介绍西门子SOMATOM CT高压发生器的工作原理,并着重分析了高压63A熔断丝炸裂故障原因及其判断与排除方法。文章指出了在检修高压发生器的过程中特别要注意的事项。