Fast- and slow-twitch isoforms (SERCA1 and SERCA2a) of sarcoplasmic reticulum Ca-ATPase are expressed simultaneously in chronically stimulated muscle fibers

 Using an immunohistochemical double-labeling technique, we observed that different isoforms of sarcoplasmic reticulum Ca-ATPase are co-expressed in single fibers of canine fast-twitch skeletal muscles stimulated chronically at low frequency. By 7 days of neuromuscular stimulation, the population of hybrid fibers expressing both SERCA1 and SERCA2a [fast- and slow-twitch isoforms of sarco(endo)plasmic reticulum Ca²⁺-ATPase] had increased from 1.5% to 9.2% of fibers. By 14 days of stimulation 90% of the pure fast-twitch fibers (expressing only SERCA1) were replaced by hybrid fibers. An additional 28 days of stimulation caused all fast-twitch fibers to express SERCA2a at the same level as found in nonstimulated slow-twitch fibers (expressing only SERCA2a). At this time, one-half of the previously hybrid fibers had become pure slow-twitch fibers. The remaining one-half of the hybrid fibers expressed SERCA1 at a very low level. Extending stimulation to 70 days did not further change the percentage of fibers that were slow-twitch or hybrid. Immunoblot studies at the whole-muscle level confirmed that changes in SERCA expression at 42 days of neuromuscular stimulation were complete. Immunohistochemical analysis of longitudinal sections of muscle showed that the changes in SERCA protein were uniform along the length of the muscle fiber, indicating that nuclei along its length responded equally to chronic stimulation. Received: 12 November 1996 / Received after revision and accepted: 16 December 1996     

The β2-agonist salbutamol affects the expression of phospholamban and both isoforms of SERCA in canine skeletal muscle and blocks changes in these induced by neuromuscular stimulation

 Chronic administration of salbutamol induced expression of hybrid fibers in canine skeletal muscles. Fast-twitch fibers expressed SERCA2a (the slow-twitch isoform of sarcoplasmic reticulum Ca²⁺-ATPase) and slow-twitch fibers expressed SERCA1 (the fast-twitch isoform of the Ca²⁺-ATPase). The proportion of fibers that became hybrid increased from a small percentage in the control muscles to 30% in the predominantly fast-twitch latissimus dorsi and to 45% in the predominantly slow-twitch vastus intermedius. In contrast to this response by the SERCA genes the phospholamban gene response was muscle specific. The fraction of fibers that expressed phospholamban decreased slightly in the latissimus dorsi while increasing moderately in the vastus intermedius. The effects of chronic neurostimulation of the latissimus dorsi on SERCA1, SERCA2a and phospholamban levels were mostly blocked by salbutamol. While 100% of fibers from neurostimulated muscles expressed phospholamban, only 51% of the fibers from the neurostimulated and salbutamol-treated muscles expressed it. In the neurostimulated muscle, very few muscle fibers expressed SERCA1a while 61% of the fibers that received salbutamol expressed it, albeit as hybrid fibers. The levels of SERCA2a in response to these interventions were just the opposite. In the neurostimulated muscle 37.5% of fibers were hybrid and 62.5% expressed SERCA2a only. With co-administration of neurostimulation and salbutamol, 61.3% of fibers were hybrid and 38.7% expressed SERCA2a only. Received: 4 July 1997 / Received after revision: 16 October 1997 / Accepted: 30 October 1997     

Thyroid Hormones and Cardiovascular Function and Diseases

Thyroid hormone (TH) receptors are present in the myocardium and vascular tissue, and minor alterations in TH concentration can affect cardiovascular (CV) physiology. The potential mechanisms that link CV disease with thyroid dysfunction are endothelial dysfunction, changes in blood pressure, myocardial systolic and diastolic dysfunction, and dyslipidemia. In addition, cardiac disease itself may lead to alterations in TH concentrations (notably, low triiodothyronine syndrome) that are associated with higher morbidity and mortality. Experimental data and small clinical trials have suggested a beneficial role of TH in ameliorating CV disease. The aim of this review is to provide clinicians dealing with CV conditions with an overview of the current knowledge of TH perturbations in CV disease.     

左室射血分数正常患者右室心尖起搏后心力衰竭相关基因表达水平变化的研究

目的：右室心尖(RVA)起搏可导致心室重构及心力衰竭。本研究探讨RVA起搏是否引起心力衰竭相关的基因表达水平的变化。 方法：选取80例因三度房室传导阻滞行永久起搏器植入术的心功能正常患者，随机1:1分为右室心尖起搏组和右室间隔部(RVS)起搏组，术前抽取外周血，测定心肌肌浆网Ca2+-ATP酶(SERCA)和 视神经萎缩症蛋白(OPAl)的mRNA表达水平，测定NT-proBNP，行超声心动图检查。术后1、6及12个月进行常规起搏器随访,并测定SERCA和 OPAl的mRNA表达水平，测定NT-proBNP，行超声心动图检查。 结果：与术前比较，RVA起搏组术后1月，6月及12月SERCA和OPA1 mRNA表达水平明显下降(P均<0.05)，起搏器植入术后12月，RVA和RVS组间SERCA、OPA1 mRNA表达水平差异有统计学意义(P=0.028；P=0.034)。RVA起搏组术后12月与术前比较，LVEF值下降有统计学差异(P=0.012)，而RVS起搏组LVEF值下降无统计学差异(P>0.05)。与术前比较，RVA起搏组术后12月的SERCA 和OPA1 mRNA表达水平变化与LVEF值变化呈正相关（r=0.529，95％ CI：0.113-0.287, P=0.017；r=0.495，95％CI：0.028-0.788，P=0.044)。RVA起搏术后12月心功能减低组的SERCA、OPAl的mRNA表达水平较无心功能减低组明显下降，差异有统计学意义（P=0.022；P=0.035）。 结论：RVA起搏术后外周血SERCA、OPAl的mRNA表达水平发生变化，这种基因表达水平的变化先于心脏结构及功能改变，而且可能与心功能减低相关。     

Therapeutic Benefit and Gene Network Regulation by Combined Gene Transfer of Apelin,FGF2, and SERCA2a into Ischemic Heart

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Arrhythmogenesis Toxicity of Aconitine Is Related to Intracellular Ca2+ Signals

Aconitine is a well-known arrhythmogenic toxin and induces triggered activities through cardiac voltage-gated Na⁺ channels. However, the effects of aconitine on intracellular Ca²⁺ signals were previously unknown. We investigated the effects of aconitine on intracellular Ca²⁺ signals in rat ventricular myocytes and explored the possible mechanism of arrhythmogenic toxicity induced by aconitine. Ca²⁺ signals were evaluated by measuring L-type Ca²⁺ currents, caffeine-induced Ca²⁺ release and the expression of NCX and SERCA2a. Action potential and triggered activities were recorded by whole-cell patch-clamp techniques. In rat ventricular myocytes, the action potential duration was significantly prolonged by 1 µM aconitine. At higher concentrations (5 µM and 10 µM), aconitine induced triggered activities and delayed after-depolarizations (6 of 8 cases), which were inhibited by verapamil. Aconitine (1 µM) significantly increased the I_Ca-L density from 12.77 ± 3.12 pA/pF to 18.98 ± 3.89 pA/pF (n=10, p<0.01). The activation curve was shifted towards more negative potential, while the inactivation curve was shifted towards more positive potential by 1 μM aconitine. The level of Ca²⁺ release induced by 10 mM caffeine was markedly increased. Aconitine (1 µM) increased the expression of NCX, while SERCA2a expression was reduced. In conclusion, aconitine increased the cytosolic [Ca²⁺]_i by accelerating I_Ca-L and changing the expression of NCX and SERCA2a. Then, the elevation of cytosolic [Ca²⁺]_i induced triggered activities and delayed after-depolarizations. Arrhythmogenesis toxicity of aconitine is related to intracellular Ca²⁺ signals.     

MicroRNA-328 as a regulator of cardiac hypertrophy

Cardiac hypertrophy is a primary predictor of progressive heart disease that often results in heart failure. Growing evidence has demonstrated that microRNAs (miRNAs) play a critical role in regulating cardiac hypertrophy. This study was designed to evaluate the effect of miR-328 on cardiac hypertrophy and the potential molecular mechanisms. We found that transgenic overexpression of miR-328 in the heart induced cardiac hypertrophy in mice, which was accompanied by reduced SERCA2a level increased intracellular calcium concentration and calcineurin protein level, and enhanced NFATc3 nuclear translocation. However, normalization of miR-328 level by its antisense chemically modified with locked nucleic acid (LNA-antimiR-328) reversed the changes. Forced expression of miR-328 resulted in cardiomyocyte hypertrophy in cultured neonatal rat ventricular cells, which was accompanied by downregulation of SERCA2a expression and activation of the calcineurin/NFATc3 signaling pathway. These changes were abolished by LNA-antimiR-328. We validated the SERCA2a as a direct target for miR-328. MiR-328 expression was upregulated in cardiomyocyte treated with isoproterenol (ISO) to induce hypertrophy; while knockdown of miR-328 attenuated the hypertrophic responses. The level of miR-328 was significantly elevated in a mouse model of hypertrophy by thoracic aortic banding (TAC). Consistently, SERCA2a was downregulated, whereas calcineurin were upregulated, and NFATc3 nuclear translocation was enhanced. In contrast, hypertrophy in these mice was significantly alleviated when treated with miR-328 antisense. MiR-328 promotes cardiac hypertrophy by targeting SERCA2a. Our study therefore uncovered a novel molecular mechanism for cardiac hypertrophy and indicated miR-328 as a potential therapeutic target for this cardiac condition.