Quinn F R, Currie S, Duncan A M, Miller S, Sayeed R, Cobbe S M, Smith G L
Division of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK.
J Physiol. 2003 Nov 15;553(Pt 1):229-42. doi: 10.1113/jphysiol.2003.050716. Epub 2003 Aug 29.
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.
在兔心左心室基底区域发生显著左心室功能障碍（LVD）8 - 9周后，于心肌梗死顶端区域测量钠钙交换体（NCX）的蛋白水平和活性。与假手术（sham）组相比，LVD组组织匀浆（121±11%）和纯化膜组分（143±12%）中的NCX蛋白丰度更高。LVD组的NCX mRNA也更高（126%）。在假手术组和LVD组中，与心内膜相比，心外膜膜组分中的NCX蛋白表达均较低。通过单电极电压钳记录分离心肌细胞中的跨膜电流；使用Fura - 2测量细胞内钙浓度（[Ca2+]i）。快速施加10 mmol l-1咖啡因以诱导肌浆网释放Ca2+。随后，LVD组中由NCX介导的Ca2+外流速率常数较低（为假手术组的70%）。在用250 nM Ca2+（50 mmol l-1 EGTA）透析的心肌细胞中测量NCX电流。LVD组中观察到较低的NCX电流（为假手术组的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；LVD组也存在这种跨壁差异。尽管蛋白表达增加，但活性降低可能是由于NCX变构调节的Ca2+敏感性降低所致。然而，测量结果表明LVD组中Ca2+敏感性增加。LVD心脏的心肌细胞横管面积显著减小（为假手术组的59%），表面积/体积比也减小（为假手术组的80%）。尽管LVD中蛋白表达增加，但横管结构破坏可能导致NCX活性降低。
