Sarcoplasmic reticulum Ca 2+ load in human heart failure

Excitation-contraction coupling and intracellular Ca ²⁺ homeostasis are altered in heart failure. We tested the hypothesis that these changes are related to disturbed Ca ²⁺ handling of the sarcoplasmic reticulum (SR). Isolated, electrically stimulated trabeculae were obtained from end-stage failing (NYHA IV) and nonfailing human hearts. Isometric twitch tension, intracellular Ca ²⁺ transients (aequorin method) and SR Ca ²⁺ content (rapid cooling contractures) were assessed under basal conditions (1 Hz, 37 °C) as well as after stepwise increasing rest intervals from 2 – 240 s (post-rest contractions). Protein expression of SERCA2a and phospholamban (Western blot) was assessed in a subset of failing trabeculae. In addition, the effects of SERCA1 overexpression on contractile function of isolated myocytes was tested. On average, post-rest twitch tension continuously increased with increasing rest intervals in nonfailing, but declined with rest intervals longer than 15s in failing myocardium. The rest-dependent contractile changes were accompanied by parallel changes in intracellular Ca ²⁺ transients. Failing trabeculae (n = 40) were grouped (group A: post-rest potentiation (force of contraction > pre-rest twitch force) after 120s rest interval; group B: post-rest decay (force of contraction < pre-rest twitch force) after 120 s rest interval), and post-rest contractile function was related to SERCA2a and PLB expression. While PLB protein expression was not different, SERCA2a protein expression as well as SERCA2a/PLB ratio was significantly higher in group A vs. group B. Transfection of SERCA1 increased shortening amplitude and enhanced relaxation kinetics in failing human myocytes. In conclusion, SR Ca ²⁺ handling is severely altered in human heart failure. Reduced SR Ca ²⁺ release is due to diminished SR Ca ²⁺ content directly related to a depressed expression of SERCA2a protein. Enhancing SERCA function or expression may improve SR Ca ²⁺ handling in failing human myocardium.     

Altered phosphatase activity in heart failure, influence on Ca 2+ movement

Many cardiac proteins undergo reversible phosphorylation. While the protein kinases which bring about phosphorylations are well studied, less effort has been put into the dephosphorylating phosphatases (for an earlier review compare 14). An important event in the heart, which is controlled by phosphorylation, is the uptake of Ca ²⁺ by the sarcoplasmic reticulum (SR). This process is brought about by a SR Ca ²⁺ ATPase (SERCA) and accounts for relaxation. The amount of Ca ²⁺ pumped by SERCA is enhanced when phospholamban (PLB), an intrinsic protein of the SR, is phosphorylated and is diminished when PLB is dephosphorylated. PLB is dephosphorylated by protein phosphatases (PPs) like PP1. As the activity of PP1 is enhanced in heart failure, subsequent dephosphorylation by of, e.g., PLB may explain the impaired relaxation of the human heart. Thus, PPs may play an important role in the etiology and/or symptoms of heart failure.     

Targeting Ca 2+ cycling proteins and the action potential in heart failure by gene transfer

Cardiomyocytes isolated from failing human hearts are characterized by contractile dysfunction including prolonged relaxation, reduced systolic force and elevated diastolic force. These contractile abnormalities are paralleled by abnormal Ca ²⁺ homeostasis such as reduced sarcoplasmic reticulum (SR) Ca ²⁺ release, elevated diastolic Ca ²⁺ and reduced rate of Ca ²⁺ removal. In addition, failing human myocardium is characterized by a frequency-dependent decrease in systolic force and Ca ²⁺ as opposed to normal myocardium where an increase in pacing rate results in potentiation of contractility and an increase in SR Ca ²⁺ release. In the failing heart, the decrease in SR Ca ²⁺ load has been linked to a decrease in SR Ca ²⁺ ATPase (SERCA2a) function. We have recently shown that overexpression of SERCA2a by adenoviral gene transfer restores contractile function in cardiac myocytes from failing human hearts. In addition, we have shown that overexpression of SERCA2a in a model of pressure-overload hypertrophy in transition to failure improves contractile function and reserve in these animals. We are currently exploring the effect of long-term expression of SERCA2a in failing animals along with the energy cost of SERCA2a expression using NMR methods. We are also using a different strategy to improve SR Ca ²⁺ ATPase activity which involves decreasing the expression of phospholamban by antisense strategies to enhance SR Ca ²⁺ ATPase activity. The Na/Ca exchanger is also being targeted to enhance calcium removal in failing hearts. Action potential prolongation is attributed to reductions in transient outward current (Ito) density in human heart failure. This prolongation can alter contractility but can also cause afterdepolarization. Using gene transfer of various K channels responsible for Ito, we are investigating the molecular and the ionic basis of action potential prolongation in cardiac hypertrophy and failure and we are examining how intracellular calcium handling changes in response to alterations in action potential duration. Gene transfer, which serves initially as an experimental tool, may provide a novel therapeutic approach.     

Voltage-gated Ca 2+ currents in the human pathophysiologic heart: a review

The L-type Ca ²⁺ current (I _Ca-L) plays a key role in the cardiac excitation-contraction (E-C) coupling. Thus, it is a major target for many transmitters and hormones modulating cardiac function and, therefore, for pharmacological drugs to regulate inotropy. Ca ²⁺ (and other) ion currents are commonly studied in animal tissues for practical reasons. Investigations in human cardiomyocytes started extensively only ten years ago with the development of patch-clamp techniques, enzymatic cell dissociation procedures, and surgical techniques. These studies have already provided valuable information concerning the nature, biophysics, pharmacology and regulation of human cardiac ionic currents in normal and diseased tissues. Interesting advances have been made to understand the role of I _Ca-L in the development of chronic atrial fibrillation (AF). Alterations of single channel activity and regulation of macroscopic I _Ca-L have also been found in heart failure (HF), although some of the data are divergent and puzzling. The T-type Ca ²⁺ current (I _Ca-T) has never been recorded in human cardiomyocytes. After a rapid overview of the basic properties of human cardiac Ca ²⁺ currents, we focus on selected aspects of pathophysiology that are still unsolved.     

Increased cardiomyocyte function and Ca2+ transients in mice during early congestive heart failure

End-stage heart failure is believed to involve depressed cardiomyocyte contractility and Ca2+ transients. However, the time course of these alterations is poorly understood. We examined alterations in myocyte excitation-contraction coupling in a mouse model of early congestive heart failure (CHF) following myocardial infarction. One week after myocardial infarction was induced by ligation of the left coronary artery, CHF mice were selected based on established criteria (increased left atrial diameter, increased lung weight). Sham-operated animals (SHAM) served as controls. Echocardiographic measurements showed decreased global function in early CHF relative to SHAM, but increased local function in viable regions of the myocardium which deteriorated with time. Cardiomyocytes isolated from the non-infarcted septum also exhibited larger contractions in early CHF than SHAM (CHF=219.6+/-15.3% of SHAM values, P<0.05; 1 Hz field stimulation), and relaxation was more rapid (time to 50% relaxation=82.9+/-5.5% of SHAM values, P<0.05). Ca2+ transients (fluo-4 AM) were larger and decayed more rapidly in CHF than SHAM during both field stimulation (1 Hz) and voltage-clamp steps. Sarcoplasmic reticulum (SR) Ca2+ content was increased. Western blots showed that while SR Ca2+ ATPase (SERCA) expression was unaltered in CHF, phospholamban (PLB) was downregulated (60+/-11% of SHAM values, P<0.05). Thus, an increased SERCA/PLB ratio in CHF may promote SR Ca2+ re-uptake. Additionally, peak L-type Ca2+ current and Na+/Ca2+ exchanger expression were increased in CHF, suggesting increased sarcolemmal Ca2+ flux. Thus, in early CHF, alterations in Ca2+ homeostasis improve cardiomyocyte contractility which may compensate for loss of function in the infarction area.     

Ca2+-handling in heart failure – a review focusing on Ca2+ sparks

[Ca ²⁺] _i-transients have been shown to be altered in isolated ventricular myocytes from terminally failing human myocardium. It has been demonstrated that one reason for this alteration is a reduction in the Ca ²⁺ content of the sarcoplasmic reticulum (SR). Further investigations were done to investigate, whether there may be an additional defect of the Ca ²⁺-release mechanisms from the SR. These release mechanisms were investigated through the recording of Ca ²⁺ sparks in single human myocytes. In cardiac myocytes, Ca ²⁺ sparks are elementary units of Ca ²⁺ release, which occur spontaneously, or which are triggered by Ca ²⁺ influx through L-type Ca ²⁺-channels (Ca ²⁺-induced Ca ²⁺ release). Ca ²⁺ sparks have been investigated in various animal models of cardiac hypertrophy and cardiac failure and results were conflicting. Discrepancies may be explained by different species and also by the mechanisms underlying hypertrophy and heart failure. This review summarizes our current knowledge on Ca ²⁺ sparks in heart failure.     

Role of Ca2+ channel in development of tension in heart muscle

Role of Ca2+ Channel in Development of Tension in Heart Muscle. Journal of Molecular and Cellular Cardiology (1987) 19, 527-553. In mammalian and amphibian hearts Ca2+ enters the myocardial cells via voltage-gated Ca2+ channels. The role of Ca2+ channels in transporting the activator Ca2+ was probed by examining the redevelopment of tension and ICa in voltage-clamped myocardial strips after step recovery of Ca2+ channel from photolabile Ca2+ antagonist. Comparison of the kinetics of redevelopment of tension in the frog and mammalian heart following the photoinactivation of Ca2+ channel blockers showed that in the frog heart tension redevelops fully in one beat, while 5 to 7 beats were required for full redevelopment of tension in the mammalian heart. Ca2+ depletion studies using Antipyrylazo III showed that extracellular Ca2+ depletion during the action potential occurs primarily via the Ca2+ channel. In the frog heart sufficient Ca2+ is transported from the extracellular space during a single beat to activate tension. In the mammalian heart ICa triggers the release of internal stores, which when only fully loaded caused full development of tension. ICa also was involved in loading the intracellular Ca2+ pools. Two types of Ca2+ channels have been identified in the mammalian myocytes. The low-threshold rapidly inactivating Ca2+ channels appear to be involved in trigger release of Ca2+, while the high threshold (conventional Ca2+ channels) seem to be involved primarily in reloading of internal Ca2+ pools.     

普鲁卡因胺、利多卡因和普罗帕酮对豚鼠心室肌细胞Na^＋／Ca^2＋交换电流的抑制作用

目的利用膜片钳技术观察Ⅰ类抗心律失常药物普鲁卡因胺、利多卡因、普罗帕酮对Na+/Ca2+交换电流的直接作用.方法采用胶原酶消化的成年大鼠单个心室肌细胞及全细胞膜片钳技术,记录Na+/Ca2+交换电流并观察药物对它的影响.结果3种药物对Na+/Ca2+交换电流的抑制均呈剂量依赖性,但抑制程度不同,其中普鲁卡因胺抑制作用最强.50、100μM的普鲁卡因胺分别使外向Na+/Ca2+交换电流从对照值(181±22)pA降低至(125±19)、(109±20)pA,内向电流由对照值(172±18)pA分别降低至(137±13)、(121±12)pA;50、100μM的利多卡因使外向电流从对照值(170±15)pA分别降低至(139±15)、(127±10)pA,内向电流由对照值(165±15)p/A分别降至(142±16)、(129±20)pA;50、100μM的普罗帕酮使外向电流由对照值(160±23)pA分别降至(130±27)、(112±26)pA,内向电流由对照值(169±13)pA分别降至(143±13)、(134±14)pA.普鲁卡因胺、普罗帕酮对外向电流的抑制大于内向电流,而利多卡因对内、外向电流的抑制差异无显著性.结论Ⅰ类抗心律失常药物对心室肌细胞Na+/Ca2+交换电流具有直接抑制作用,且抑制程度不同.     

Role of Ca2+ availability to myofilaments and their sensitivity to Ca2+ in myocyte contractile dysfunction in heart failure

OBJECTIVE: Contractile function is depressed at the isolated myocyte level in heart failure (HF), which could result from the decreased availability of intracellular calcium ([Ca2+]i) to the myofibrils and/or the depressed sensitivity of myofilaments to [Ca2+]i. However, the cellular basis of contractile dysfunction remains unestablished. METHODS: We isolated left ventricular myocytes from dogs with rapid pacing-induced HF. Cell shortening and [Ca2+]i transients were measured by indo-1 fluorescence and the myofilament Ca2+ sensitivity was analyzed by the shortening-[Ca2+]i relation in intact myocytes as well as by the pCa tension relation in skinned cells. RESULTS: Peak cell shortening magnitude was depressed in HF, associated with a parallel decrease of [Ca2+]i transient amplitude. There was a significant positive correlation between these two variables (r = 0.71, P < 0.01). In contrast, myofibrillar sensitivity to Ca2+, determined by both intact and skinned myocytes, was comparable between control and HF. Further, there was no significant difference in Ca2+ sensitivity between control and HF even at shorter (1.8 microns) or longer (2.2 microns) sarcomere length. CONCLUSIONS: Using both intact and skinned cellular preparations, a potential defect in myocyte contractile function in HF was a reduction in Ca2+ availability to the myofilaments, rather than the inherent defects in myofilament sensitivity to Ca2+.     

增龄对人体外周血CD4+CD25+Foxp3+调节T细胞、CD4+T细胞及细胞因子表达的影响

目的探讨增龄对人体外周血CD4⁺CD25⁺Foxp3⁺调节T细胞(CD4⁺CD25⁺Foxp3⁺Treg)、CD4⁺T细胞及细胞因子表达的影响。方法选择青年人(20~45岁)、中老年人(50~75岁)及高龄老年人(≥80岁)各40例,分别检测3组外周血CD4⁺T、CD4⁺CD25⁺Foxp3⁺Treg的绝对计数,并计算后者占前者的百分比,同时检测并比较3组人群外周血IL-2、干扰素-γ(IFN-γ)、TNF-α、IL-10和IL-17水平。结果高龄老年组CD4⁺T细胞绝对计数较中老年组与青年组显著下降(P<0.05);高龄老年组和中老年组外周血CD4⁺CD25⁺Foxp3⁺Treg绝对计数均明显高于青年组(P<0.05);中老年组CD4⁺CD25⁺Foxp3⁺Treg占CD4⁺T细胞百分比明显高于青年组,高龄老年组明显高于中老年组,差异均有统计学意义(P<0.05)。高龄老年组IL-2、IFN-γ和IL-17水平明显低于青年组和中老年组(P<0.05),中老年组IL-2明显低于青年组(P<0.05),高龄老年组IL-10水平明显高于青年组和中老年组(P<0.05),3组TNF-α水平差异无统计学意义(P>0.05)。结论中老年以后人体外周血CD4⁺CD25⁺Foxp3⁺Treg绝对计数明显增高,随着增龄,其占CD4⁺T细胞百分比逐渐升高。高龄老年人外周血CD4⁺T细胞绝对计数、IL-2、IFN-γ和IL-17水平明显下降,IL-10水平明显增高,说明老年人免疫功能进一步下降,衰老的微环境发生了改变。     

COPD患者CD4+/CD8+、CD8+CD28+ T淋巴细胞检测意义

目的分析慢性阻塞性肺疾病(COPD)患者CD4⁺/CD8⁺、CD8⁺CD28⁺调节性T淋巴细胞检测意义。 方法收集2018年6月至2019年6月于我院就诊收治的98例COPD患者的临床资料,随访18个月,根据患者生存情况分为存活组85例与死亡组13例,采用流式细胞术检测COPD患者CD4⁺/CD8⁺、CD8⁺CD28⁺调节性T淋巴细胞,应用ROC曲线分析CD4⁺/CD8⁺及CD8⁺CD28⁺调节性T淋巴细胞预测COPD患者死亡的价值。 结果两组患者PaO₂、FEV₁占预测值、有创机械通气例数所占比、CD4⁺/CD8⁺以及CD8⁺CD28⁺ T淋巴细胞占比存在统计学差异(P<0.05);多因素Logistic回归分析,PaO₂、FEV₁占预测值、有创机械通气、CD4⁺/CD8⁺、CD8⁺CD28⁺是COPD预后的独立危险因素(P<0.05);CD4⁺/CD8⁺、CD8⁺CD28⁺ T淋巴细胞水平预测COPD患者死亡的最佳截断值分别为1.76%、7.85%,二者联合预测COPD患者死亡的ROC曲线下面积(AUC)为0.913(95%CI: 0.862~0.947),明显高于单项CD4⁺/CD8⁺的AUC值(0.784, 95%CI: 0.602~0.850)及CD8⁺CD28⁺的AUC值(0.795,95%CI：0.596~0.861)。 结论COPD患者CD4⁺/CD8⁺、CD8⁺CD28⁺ T淋巴细胞与患者预后密切相关,二者联合检测对COPD患者预后有意义。     

Altered regulation of cardiac contraction and relaxation by Ca2+ in heart failure

Myocardial contractile dysfunction in congestive heart failure is characterized by a decrease in force developed and retardation of relaxation. These alterations are mainly due to those in intracellular Ca(2 +) transients (CaT) . CaT are regulated by a number of functional proteins, including sarcolemmal L-type Ca(2 +) channels, Na(+)/Ca(2 +) exchanger and Ca(2 +) ATPase, sarcoplasmic reticulum Ca(2 +) ATPase (SERCA 2 ) , phospholamban and ryanodine receptors, and mitochondrial Ca(2 +) uniporter. Changes in expression and function of these regulatory proteins that occur in the course of increasing severity of heart failure are responsible for the characteristic changes in force development and relaxation observed under pathophysiological conditions in congestive heart failure.     

Increased Ca2+-sensitivity of the contractile apparatus in end-stage human heart failure results from altered phosphorylation of contractile proteins

OBJECTIVE: The alterations in contractile proteins underlying enhanced Ca(2+)-sensitivity of the contractile apparatus in end-stage failing human myocardium are still not resolved. In the present study an attempt was made to reveal to what extent protein alterations contribute to the increased Ca(2+)-responsiveness in human heart failure. METHODS: Isometric force and its Ca(2+)-sensitivity were studied in single left ventricular myocytes from non-failing donor (n=6) and end-stage failing (n=10) hearts. To elucidate which protein alterations contribute to the increased Ca(2+)-responsiveness isoform composition and phosphorylation status of contractile proteins were analysed by one- and two-dimensional gel electrophoresis and Western immunoblotting. RESULTS: Maximal tension did not differ between myocytes obtained from donor and failing hearts, while Ca(2+)-sensitivity of the contractile apparatus (pCa(50)) was significantly higher in failing myocardium (deltapCa(50)=0.17). Protein analysis indicated that neither re-expression of atrial light chain 1 and fetal troponin T (TnT) nor degradation of myosin light chains and troponin I (TnI) are responsible for the observed increase in Ca(2+)-responsiveness. An inverse correlation was found between pCa(50) and percentage of phosphorylated myosin light chain 2 (MLC-2), while phosphorylation of MLC-1 and TnT did not differ between donor and failing hearts. Incubation of myocytes with protein kinase A decreased Ca(2+)-sensitivity to a larger extent in failing (deltapCa(50)=0.20) than in donor (deltapCa(50)=0.03) myocytes, abolishing the difference in Ca(2+)-responsiveness. An increased percentage of dephosphorylated TnI was found in failing hearts, which significantly correlated with the enhanced Ca(2+)-responsiveness. CONCLUSIONS: The increased Ca(2+)-responsiveness of the contractile apparatus in end-stage failing human hearts cannot be explained by a shift in contractile protein isoforms, but results from the complex interplay between changes in the phosphorylation status of MLC-2 and TnI.     

疟疾感染过程中Tregs对DCs免疫功能的抑制作用与机理

目的 探讨疟疾感染过程中调节性T细胞(Treg)对DCs免疫功能的抑制作用与机理。方法 建立P.y17XL感染和Tregs消除BALB/c小鼠模型,计数红细胞感染率;感染后第0、3和5 d制备脾细胞悬液,FACS检测脾脏中DCs亚群数量变化;DCs表面分子MHC-II、CD80和CD86的表达水平及分泌IL-10的DCs数量变化。结果 与正常感染组小鼠相比,Tregs消除组小鼠于感染后第3 d DCs亚群,MHC-II,CD80和CD86的表达均明显增加,感染后第5 d DCs亚群数量、MHC-II和CD80表面分子的表达均明显减少;然而分泌IL-10的DCs数量于感染后第5 d明显增加,是同天感染鼠的3.5倍。另外,我们采用两种anti-CD25mAb体内阻断Tregs,效果有着明显的差异。7D4能长期有效的阻断CD25表达,而PC61仅能短期内维持CD25低表达。结论 P.y17XL感染早期,BALB/c小鼠Tregs数量升高与DCs功能受损具有相关性。Tregs能抑制DCs的免疫功能,这一现象可能与Tregs调控DCs的亚群、表型和细胞因子分泌模式等方面有关。