Myocardial infarction causes increased expression but decreased activity of the myocardial Na+-Ca2+ exchanger in the rabbit
Myocardial infarction causes increased expression but decreased activity of the myocardial Na+-Ca2+ exchanger in the rabbit
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DOI：
10.1113/jphysiol.2003.050716
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发表时间：
2003-11-15
影响因子：
5.5
通讯作者：
Smith, GL
中科院分区：
文献类型：
--
作者：
Quinn, FR;Currie, S;Smith, GL
本实验观察了急性心肌梗死后8-9周左室功能不全（LVD）家兔左室基底部心肌Na ~+-Ca ~（2+）交换器（NCX）蛋白水平和活性的变化。与假手术（sham）组相比，LVD中组织匀浆（121 +/-11%）和纯化膜组分（143 +/-12%）中的NCX蛋白丰度更高。NCX mRNA在LVD组中也较高（126%）。在假手术组和LVD组中，与心内膜相比，在心外膜的膜组分中观察到较低的NCX蛋白表达。通过单电极电压钳记录分离的心肌细胞中的跨膜电流;使用Fura-2测量[Ca 2 +]（i）。快速应用10 mmol l（-1）咖啡因用于诱导肌浆网释放Ca 2+。LVD组随后的NCX介导的Ca 2+外排速率常数较低（假手术组的70%）。在用250 nm Ca 2+（50 mmol l（-1）EGTA）透析的心肌细胞中测量NCX电流。在LVD组中观察到较低的NCX电流（假手术的75%）。与心内膜相比，从心外膜分离的心肌细胞中也观察到较低的NCX活性;在LVD组中也观察到透壁差异。尽管蛋白质表达增加，但活性降低可能是由于NCX变构调节的Ca 2+敏感性降低。然而，测量结果表明LVD组的Ca 2+敏感性增加。来自LVD心脏的心肌细胞显示横小管面积（假手术组的59%）和表面积/体积比（假手术组的80%）显著减少。尽管LVD中的蛋白表达增加，但横小管结构的破坏可能导致NCX活性的降低。
Na+-Ca2+ exchanger (NCX) protein levels and activity were measured in myocardium from the basal region of the left ventricle of rabbit hearts with significant left ventricular dysfunction (LVD), 8-9 weeks after an apical infarction. NCX protein abundance was higher in the tissue homogenates (121 +/- 11 %) and purified membrane fractions (143 +/- 12 %) in the LVD compared to the sham-operated (sham) group. NCX mRNA was also higher in the LVD group (126 %). Lower NCX protein expression was observed in the membrane fractions from the epicardium compared to the endocardium in both the sham and LVD groups. Transmembrane currents were recorded in isolated cardiomyocytes by single-electrode voltage clamp; [Ca2+](i) was measured using Fura-2. Rapid application of 10 mmol l(-1) caffeine was used to induce Ca2+ release from the sarcoplasmic reticulum. The subsequent NCX-mediated Ca2+ efflux rate constant was lower (70 % of sham) in the LVD group. NCX currents were measured in cardiomyocytes dialysed with 250 nm Ca2+ (50 mmol l(-1) EGTA). A lower NCX current (75 % of sham) was observed in the LVD group. Lower NCX activity was also observed in cardiomyocytes isolated from the epicardium compared to the endocardium; a transmural difference that was also seen in the LVD group. Reduced activity despite increased protein expression may result from reduced Ca2+ sensitivity of the allosteric regulation of NCX. However, measurements indicated increased Ca2+ sensitivity in the LVD group. Cardiomyocytes from LVD hearts displayed a marked reduction in the transverse tubule area (59 % of sham) and the surface area/volume ratio (80 % of sham). Disrupted transverse tubule structure may contribute to the decrease in NCX activity despite increased protein expression in LVD.