The ionic mechanisms of long QT interval in diabetic rabbits

Objective Abnormal QT prolongation associated with arrhythmias is considered the major cardiac electrical disorder and a significant predictor of mortality in diabetic patients. The precise ionic mechanisms for diabetic QT prolongation remained unclear. The present study was designed to analyze the changes of ventricular repolarization and the underlying ionic mechanisms in diabetic rabbit hearts. Methods Diabetes was induced by a single injection ofalloxan （145mg/kg, Lv. ）. After the development of diabetes （10 weeks）, ECG was measured. Whole-cell patch-clamp technique was applied to record the action potential duration （APD50, APD90）, slowly activating outward rectifying potassium current （IKs）, L-type calcium current （ICa-L） and inward rectifying potassium current （IK1）. Results The action potential duration （APD50 and APD90） of ventricular myocytes was obviously prolonged from 271.5＋32.3 ms and 347.8＋36.3 ms to 556.6~72.5 ms and 647.9~72.2 ms respectively （P〈 0.05）. Meanwhile the normalized peak current densities of IKs in ventricular myocytes investigated by whole-cell patch clamp was smaller in diabetic rabbits than that in control group at test potential of＋50mV （1.27~0.20 pA/pF vs 3.08~0.67 pA/pF, P〈0.05）. And the density of the ICa-L was increased apparently at the test potential of 10 mV （-2.67~0.41 pA/pF vs -5.404-1.08 pA/pF, P〈0.05）. Conclusion Ventricular repolarization was prolonged in diabetic rabbits, it may be partly due to the increased L-type calcium current and reduced slow delayed rectifier K＋ current （IKs） （J Geriatr Cardio12010; 7：25-29）.     

Functional remodeling of Ca2+-activated Cl-channel in pacing induced canine failing heart

To determine whether Ca²⁺ activated Cl^-current (I_Cl（Ca）) contributes to the functional remodeling of the failing heart. Methods Whole cell patch-clamp recording technique was employed to record the I_Cl（Ca） in cardiac myocytes enzymatically isolated from rapidly pacing induced canine failing hearts at room temperature and compared that of the normal hearts （Nor）.Results The current density of DIDS （200M） sensitive I_Cl（Ca） induced by intracellular Ca²⁺ release trigged by L-type Ca²⁺ current (I_Ca,L) was significantly decreased in heart failare （HF） cells compared to Nor cells.At membrane voltage of 20mV,the I_Cl（Ca） density was 3.02±0. 54 pA/pF in Nor （n=6） vs.1.31±0.25 pA/pF in HF （n=8） cells,（P<0.01）,while the averaged I_Ca,L density did not show difference between two groups.The time constant of current decay of I_Cl（Ca） was similar in both types of cells.On the other hand,in intra cellular Ca²⁺ clamped mode,where the [Ca²⁺]_i was maintained at 100nmol/L,I_Cl（Ca） density be increased significantly in HF cells when the membrane voltage at +30mV or higher.Conclusions Our results suggest that I_Cl（Ca） density was decreased in pacing induced failing heart but the channel function be enhanced.Impaired Ca²⁺ handing in HF cells rather than reduced I_Cl（Ca） channel function itself may have caused this abnormality.The I_Cl（Ca） density reduction might contribute to the prolongation of action potential in failing heart.The I_Cl（Ca） channel function up-regulation is likely to cause cardiac arrhythmia by inducing a delayed after depolarization,when Ca²⁺ overload occurred in diastolic failing heart cells.     

Effects of Angiotensin Ⅱ and ACE Inhibitor,Captopril on L-type Calcium Current and Sodium Current of Single Guinea Myocytes

Objectives To investigate effect of Angll, captopril on single guinea myocytes on L - type calcium current and sodium current. Methods Membrane patch clamp whole cell recording technique was used to investigate effect of angll, captopril on L - Ca maximum current density and sodium maximum current density. Resutls Angll increased the maximum current density compared with control after perfused 5 min, 357. 7 ±219. 7 Vs 279. 5± 240. 5 PA/PF, increase rate is 27. 9 %, the shape of current - voltage relationship curve was unchanged, peaked at 10 mv, indicated that angll increased L - Ca current density in voltage - dependent. After perfused with captopril, captopril angll 3, 5 min, L - Ca current was recorded, results suggest L - Ca maximum current density decreased significantly compared with control, in captopril group, 128. 4 ± 92. 6Vs286. 2 ± 89. 7, 66. 7±68. 3Vs 286. 2 ± 89. 7, respectively, rate of inhibition is 55. 1 %, 76. 6 %, respectively. L - Ca current further decreased in captopril pe     

硫化氢对离体大鼠心室肌细胞ATP依赖的钾通道外向电流的影响

Objective To investigate the effects of endogenous and exogenous hydrogen sulfide (H2S) on the KATP current in isolated rat ventricular myoeytes. Methods Ventrieular myoeytes were isolated from rat heart by modified Langendoff perfusion with collagenase. KATP current of single rat ventricular myocytes was recorded by whole-cell patch-clamp technique. Results The density of KATP current was significantly reduced by 200 μmol/L DL-propargylglyeine (PPG, an irreversible inhibitor of the H2S) [(5.3258±0.7556) pA/pF vs. (3.7856±0.4312) pA/pF, P ＜ 0.01] in a time-dependent way. The density of KATP current could be significantly increased by NariS(a H2S donor, 9.375, 18.75, 37.5,75, 150 μmol/L) in a concentration-dependent manner [(6.6310±0.6092) pA/pF vs. (9.0949±1.0259)pA/pF at 150 μmol/L, P ＜ 0.01]. Conclusion Both endogenous and exogenous H2S could open KATP channels and enhance the KATP current in rat ventricular myocytes.     

Heterogeneous of potassium currents in free wall myocytes from the infarcted rabbit ventricle and regression effects of imidapril

Objective To define the heterogeneous changes of ion channels in the noninfarcted myocardium after myocardial infarction in rabbit and effects of imidapril.Mehods Rabbits with left coronary artery ligation were prepared and allowed to recover for 8 wk.Myocytes were isolated from subendocardial,midmyocardial and subepicardial regions of the noninfarcted left ventricular free wall.Ion currents were recorded with whole-cell patch clamp way.Results The densities of the transient outward K+ currents (I to) and the inward rectifier K+ currents (I K1) were greatly reduced in midmyocardium and subepicardium while two currents reduced gently in subendocardium.The densities of the delayed rectifier K+ currents (I K) were reduced in noninfarcted three layers similarly.Imidapril could reverse the changes of membrane currents in healed myocardial infarction cells and depress the dispersion of repolarization.Conclusions The heterogeneities of K currents are enhanced in noninfarcted area.Normalization of heterogeneous changes of repolarization after treatment with imidapril was observed.     

Effect of ivabradine on hyperpolarization activated cation current in canine pulmonary vein sleeve cardiomyocytes with atrial fibrillation

Objective To study the effect of ivabradine on hyperpolarization activated cation current in canine pulmonary vein(PY) sleeve cardiomyocytes with atrial fibrillation. Methods Dissociation of PVs yielded single cardiomyocytes from a Landengorff column without or with pacemaker activity from long-term rapidly atrial pacing (RAP) canines. If current was measured with the whole-cell patch-clamp technique. Results Compared with the control group, the rapidly atrial pacing canine PV cardiomyocytes had spontane- ous diastolic depolarization and had larger If densities. Ivabradine (Iva,1 μM), a selective inhibitor of the If current, markedly reduced If currents in the RAP from -2.66±0.4 pA/pF to -1.58±0.1 pA/pF at the test potential of -120 mV (P<0.01,n=12). Inhibition effect of Iva of If current showed concentration-dependent range from 0.1 to 10.0 μM, with IC50 of 2.2 μM ( 1.8-2.9 μM, 95% CL). Furthermore, V1/2 of steady-state activated curve was shifted from -84.3±4.9 mV to -106.9±3.4 mV and k value of steady-state activated curve was changed from 12.1±2.6 mV to 9.9±3.4 mV by the application of. 1.0 μM Iva ( P<0.01, n=12). Conclusions Our study revealed that Ivarbadine may significantly decrease If of rapidly atrial pacing pulmonary vein sleeve cells with atrial fibrillation.     

Effects of palmatine on potassium and calcium currents in isolated rat hepatocytes

AIM: To study the effects of palmatine, a known inhibitoron delayed rectifier potassium current and L-type calciumcurrent (ICa,L) in guinea pig ventricular myocytes, on thepotassium and calcium currents in isolated rat hepatocytes.METHODS: Tight-seal wh ole-cell patch-clamp techniqueswere performed to investigate the effects of palmatine onthe delayed outward potassium currents (IK), inward rectifierpotassium current (IK1) and Ca2+ release-activated Ca2+current (ICRAC) in enzymatically isolated rat hepatocytes.RESULTS: Palmatine 0.3-100 μM reduced IK in a concentationdependent manner with EC50of 41.62±10.11 μM and nH,0.48±0.07 (n=8). The effect of the drug was poorly reversibleafter washout. When the bath solution was changed totetraethylammonium (TEA) 8 mM, IK was inhibited.Palmatine 10 μM and 100 μM shifted the I-V curves of IKdownward, and the block of IK was voltage-independent.Palmatine 0.3-100 μM also inhibited ICRAC in a concentration-dependent manner. The fitting parameters were as follows:ECs0=51.19±15.18 μM, and nH=0.46+0.07 (n=8). The peakvalue of ICRAC in the I-V relationship was decreased bypalmatine 10 μM and 100 μM. But the reverse potential ofIcRAcoCcurred at Voltage=0 mV in all cells. Palmatine 0.3-100 μM failed to have any significant effect on either inwardor outward components of IK1 at any membrane potentialexamined.CONCLUSION: The inhibitory effects on IK and ICRAC couldbe one of the mechanisms that palmatine exerts protectiveeffect on hepatocytes.     

Effects of simvastatin on ion channel currents in ventricular myocytes from rabbit with acute myocardial infarction

Objective To investigate the effects of simvastatin on membrane ionic currents in left ventricular myocytes after acute myocardial infarction (AMI,so as to explore the ionic mechanism of statin treatment for antiarrhythmia.Methods Fourty-five New Zeland rabbits were randomly divided into three groups:AMI group,simvastatin intervention group （statin group） and sham-operated control group （CON）.Rabbits were infarcted by ligation of the left anterior descending coronary artery after administration of oral simvastatin 5 mg·kg^-1·d^-1 （Statin group） or placebo （AMI group）for 3 days.Twenty-four hours later,single ventricular myocytes were isolated enzymatically from the epicardial zone of the infracted region.Whole cell patch clamp technique was used to record membrane ionic currents,including sodium current (I_Na),L-type calcium current (I_Ca-L) and transient outward potassium current (I_to).Results①There was no significant difference in serum cholesterol concentration among three groups.②The peak I_Na current density （at-30 mV） was significantly decreased in AMI group （-23.26±5.18） compared with CON （-42.78±5.48,P<0.05）,while it was significantly increased in Statin group （-39.23±5.45） compared with AMI group （P<0.01）;The peak I_Ca-L current density （at 0 mV） was significantly decreased in AMI group （-3.23±0.91） compared with CON （-4.56±1.01,P<0.05）,while it was significantly increased in Statin group （- 4.18±0.95） compared with AMI group （P<0.05）;The I_to current density（at +60 mV） was significantly decreased in AMI group（10.41±1.93）compared with CON （17.41±3.13,P<0.01）,while it was significantly increased in Statin group（16.21±2.42）compared with AMI group （P<0.01）.Conclusions AMI induces significant down-regulation of I_Na,I_Ca-L and I_to.Pretreatment with simvastatin could attenuate this change wit     

Intestinal M cells:The fallible sentinels?

The gastrointestinal tract represents the largest mucosal membrane surface in the human body. The immune system in the gut is the first line of host defense against mucosal microbial pathogens and it plays a crucial role in maintaining mucosal homeostasis. Membranous or microfold cells, commonly referred to as microfold cells, are specialized epithelial cells of the gut-associated lymphoid tissues (GALT) and they play a sentinel role for the intestinal immune system by delivering luminal antigens through the follicle-associated epithelium to the underlying immune cells. M cells sample and uptake antigens at their apical membrane, encase them in vesicles to transport them to the basolateral membrane of M cells, and from there deliver antigens to the nearby lymphocytes. On the flip side, some intestinal pathogens exploit M cells as their portal of entry to invade the host and cause infections. In this article, we briefly review our current knowledge on the morphology, development, and function of M cells, with an emphasis on their dual role in the pathogenesis of gut infection and in the development of host mucosal immunity.     

Synthesis of prostaglandins by cultured rat hearts myocytes and cardiac mesenchymal cells

Ischemia, trauma and hormonal stimulation elicit the release of prostaglandins (PGs) from the heart. Although PGI₂ is synthesized by coronary arteries, the capacities for PG synthesis of individual types of cells comprising the heart have not been elucidated. Accordingly, synthesis of prostaglandins by cultured rat cardiac myocytes and mesenchymal cells was evaluated by radiochromatography of products obtained by incubating cells with [1-¹⁴C]arachidonate, and verified by assessing the effects of cell incubation medium on platelet aggregation. Cultured mesenchymal cells synthesized PGs E₂, F_2α and 6-keto-F_1α, a metabolite of PGI₂ (2076 ± 183, 1284 ± 158 and 1194 ± 152 dpm/mg protein/30 min, respectively). Medium from mesenchymal cells inhibited platelet aggregation, an effect abolished by preincubating the cells with indomethacin, further indicating that these cells synthesized PGI₂. Cardiac myocytes synthesized PGE₂ and PGF_2α (952 ± 227 and 287 ± 104 dpm/mg protein/30 mins, respectively), but no PGI₂. Medium from myocytes did not inhibit platelet aggregation. Prostaglandins D₂, A₂ and thromboxane were not synthesized by either type of cell. Thus, PGI₂ is synthesized by cardiac mesenchymal cells and the hitherto uncharacterized sources of PGE₂ and PGF_2α found in coronary sinus effluent may include cardiac myocytes as well as mesenchymal cells.     

成年小鼠心肌细胞的分离及电生理特性

目的 :摸索成年小鼠心肌细胞分离方法并观察其电生理特性。方法 :采用酶消化法分离单个心肌细胞 ,应用膜片钳全细胞记录技术记录钙电流和钾电流。结果 :本法分离所得心肌细胞横纹清晰 ,一次性复钙 ,可获得 5 0 %～6 0 %的耐钙细胞 ;并具有正常电生理活性 ,易于形成高阻封接 ,可用于钙电流和钾电流记录。结论 :本实验所采用的分离方法经济、简便、成功率高 ,所获细胞具有正常的电生理活性     

伊布利特对兔左室中层细胞L型钙电流的影响

目的观察伊布利特对正常心肌细胞L型钙通道电流(ICa-L)的影响。方法用全细胞膜片钳技术记录10-6,10-5mol/L伊布利特细胞外液对兔正常左室中层心肌细胞L型钙通道电流(ICa-L)活性的影响。结果①伊布利特灌流后ICa-LI-V曲线下移,低、高剂量伊布利特灌流后电流密度峰值明显增加(-8.34±2.67,-10.50±3.81pA/pFvs-5.68±1.53pA/pF,P均<0.01),且高剂量较低剂量灌流时增加更明显。②低、高剂量伊布利特灌流后失活曲线右移,且高剂量时右移更明显。高剂量时半数失活电压(V0.5)较低剂量和用药前显著降低,而低剂量与用药前无差异。三种状态的激活曲线无差异。结论伊布利特可能呈浓度依赖性影响心室肌细胞L型钙电流(ICa-L)活性。     

Influence of hypothyroidism and the reversal of hypothyroidism on hemodynamics and cell size in the adult rat heart

Hypothyroid-induced atrophy of cardiac myocytes was examined in adult female rats in an effort to correlate hemodynamic and cellular changes associated with this disorder. Additional rats were studied 6 weeks after discontinuing antithyroid treatment to determine if structural and functional changes were completely reversible. To induce hypothyroidism, rats were injected daily with propylthiouracil (PTU) for 4 weeks. Control animals were injected similarly with Tris buffer. At the end of the treatment period, hemodynamic measurements were made prior to obtaining isolated myocytes. Cell volume, length, and cross-sectional area were obtained from the septum, and left and right ventricles of treated and untreated rats. After four weeks treatment with PTU, body weight was unchanged but heart weight was significantly reduced by 24%. Characteristic hemodynamic changes associated with hypothyroidism in the rat were noted (eg. reduced heart rate, cardiac output, dP/dtmax, and ventricular pressure). Cell volume was significantly smaller in hypothyroid rats primarily due to a reduction in myocyte cross-sectional area. The hemodynamic and cellular response to hypothyroidism was similar in the right and left ventricle. Six weeks after discontinuing PTU treatment, cellular and hemodynamics changes had returned to normal. It was concluded that hypothyroidism caused a true cardiac atrophy which was reversible. Reduced myocyte cross-sectional area was responsible for most of the myocyte atrophy.     

欣力胶囊抑制Ang-Ⅱ刺激引起的心肌细胞肥大

目的欣力胶囊为中德实验室自主开发的治疗心力衰竭的药物。本实验将明确欣力胶囊是否能够抑制AngiotensinⅡ刺激引起的心肌细胞肥大。方法以欣力胶囊灌胃大鼠,7 d后取大鼠血清进行细胞水平的血清药理学实验。AngiotensinⅡ刺激原代培养的心肌细胞,分组为:正常对照、AngiotensinⅡ阳性对照、欣力胶囊对照和欣力胶囊药效观察组,其中药效观察组再按照不同剂量分为六组。培养24 h以后,通过3 h掺入实验、蛋白含量测定和细胞表面积计算三种方法确定心肌细胞肥大状态。结果AngiotensinⅡ刺激以后,细胞[3H]摄入量、蛋白含量和细胞表面积均明显增加 (P<0．01)。欣力胶囊能够显著抑制AngiotensinⅡ引起的心肌细胞肥大(vs．AngiotensinⅡ阳性对照,P<0．01)。结论欣力胶囊能够抑制AngiotensinⅡ刺激引起的心肌细胞肥大,从而抑制心肌重塑发生,可能是欣力胶囊治疗心力衰竭的机制之一。     

Autophagy in the myocardium: Dying for survival?

Autophagy is an intracellular phenomenon in which a cell digests its own constituents. Autophagy is well conserved in nature from lower eukaryotes to mammals and has been attributed to disparate physiological events - including cell death, the mechanism of which is different from apoptosis. However, unlike in apoptosis, in which a family of cysteine proteases (caspases) and a number of other regulatory proteins have been identified and characterized, the mechanism of autophagic cell death remains unclear. In addition, the general mechanisms by which autophagy is initiated and modulated are just emerging, and several lines of evidence indicate that activated class I phosphatidylinositol 3-kinase and mammalian target of rapamycin (mTOR) inhibit autophagy, while class III phosphatidylinositol 3-kinase acts as a facilitator. Autophagy has been attributed to a number of cardiac disorders, such as ischemic cardiomyopathy, cardiac hypertrophy, hemochromatosis and myocardial aging. Induction of ventricular hypertrophy is associated with decreased autophagy, whereas it is enhanced during the regression of hypertrophy. Induction of acute cardiotoxicity by the anticancer drug anthracycline is also associated with massive cardiomyocyte loss due to autophagy (and apoptosis). Myocyte loss due to autophagy has also been reported during progression from compensated hypertrophy to heart failure in a pressure-overloaded model. Although the depth and dimension of the regulatory network that modulates autophagy in mammalian cells has yet to emerge, existing evidence suggests that it is an integral part of maintaining cellular metabolism, organelle homeostasis and redox equilibrium. Thus, it is a likely possibility that autophagy plays a crucial role in maintaining healthy myocytes in the myocardium.     

Diversity of early afterdepolarizations in guinea pig myocytes: Spatial characteristics of intracellular Ca2+ concentration

Summary We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca²⁺ concentration ([Ca²⁺]_i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the current, clamp technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes (n = 26 from eight hearts) and those with heterogeneous changes (n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (–34mV) than EADs with heterogeneous features (–57 mV). These results suggest that EADs have at least two constituents.     

TNF-α介导的心肌细胞凋亡信号转导通路在心肌损伤中的作用

肿瘤坏死因子-α(TNF-α)介导心肌细胞凋亡具有双向效应,可以通过重要的三条凋亡途径促心肌细胞凋亡,同时也可通过核因子-kB、AKT等信号转导途径抑制心肌细胞凋亡,最终效应取决于局部心肌中TNF-α的浓度,现就TNF-α介导的这些重要信号转导通路及其在心肌损伤中的作用做一综述.