Kurz T, Richardt G, Hagl S, Seyfarth M, Schömig A
Department of Medicine I, Technical University, Munich, Germany.
J Mol Cell Cardiol. 1995 May;27(5):1161-72. doi: 10.1016/0022-2828(95)90052-7.
Species-related differences in the mechanisms of noradrenaline release during normoxia and myocardial ischemia emphasize the need for studies on human hearts. Therefore, the mechanisms of noradrenaline release were investigated during normoxia and energy depletion in incubated human atrial tissue and compared to the release characteristics in normoxic and ischemic rat heart. Potential differences of atrial versus ventricular myocardium were assessed by comparing catecholamine release during electrical stimulation and ischemia in isolated rat atrium with release characteristics in the intact perfused heart. The overflow of endogenous noradrenaline and its deaminated metabolite dihydroxyphenylethyleneglycol (DOPEG) were determined by high pressure liquid chromatography and electrochemical detection. During normoxia noradrenaline release was evoked by electrical field stimulation. Stimulation-induced noradrenaline release depended on the extracellular calcium concentration in both species and was almost completely suppressed under calcium-free conditions. The release was significantly inhibited by neuronal (N-type) calcium channel blockers such as omega-conotoxin (100 nmol/l) and cadmium chloride (100 mumol/l), indicating a predominant role of N-type calcium channels in exocytotic noradrenaline release from sympathetic neurons in human and rat heart. Desipramine (100 nmol/l) enhanced the overflow of noradrenaline evoked by electrical stimulation in both species by blocking neuronal catecholamine uptake (uptake1). Myocardial ischemia was caused by interruption of perfusion flow in rat heart and simulated by anoxic and glucose-free incubation in human and rat atrial tissue. Ischemia- and anoxia-induced noradrenaline release in rat heart and human atrial tissue was unaffected by varying extracellular calcium concentrations and occurred even after omission of calcium and addition of EGTA (1 mmol/l). In both species neither omega-conotoxin (100 nmol/l) nor cadmium chloride (100 mumol/l) affected ischemia-induced noradrenaline overflow in both rat heart and atrium as well as in human atrium. In human and rat atrial tissue, blockade of energy metabolism in the presence of oxygen (cyanide model) resulted in a desipramine-sensitive release of noradrenaline, which was accompanied by DOPEG overflow, indicating increased axoplasmic noradrenaline concentration. The data imply a dual mechanism of noradrenaline release in the human heart. During normoxia noradrenaline release is modulated by neuronal calcium influx indicating exocytotic release. Ischemia-induced noradrenaline release, however, is independent of calcium and inhibited by uptake1 blockade suggesting nonexocytotic release mechanism. The characteristics of noradrenaline release in human atrial tissue provide evidence for carrier-mediated release of noradrenaline from sympathetic neurons operative in the ischemic human myocardium.
在常氧和心肌缺血期间去甲肾上腺素释放机制的物种差异强调了对人类心脏进行研究的必要性。因此，研究了常氧和能量耗竭状态下培养的人心房组织中去甲肾上腺素的释放机制，并与常氧和缺血大鼠心脏的释放特征进行比较。通过比较离体大鼠心房在电刺激和缺血期间的儿茶酚胺释放与完整灌注心脏的释放特征，评估心房与心室心肌的潜在差异。内源性去甲肾上腺素及其脱氨基代谢产物二羟基苯乙二醇（DOPEG）的溢出通过高压液相色谱和电化学检测来测定。在常氧状态下，电场刺激可诱发去甲肾上腺素释放。刺激诱导的去甲肾上腺素释放在两种物种中均依赖于细胞外钙浓度，并且在无钙条件下几乎完全被抑制。这种释放被神经元（N型）钙通道阻滞剂如ω-芋螺毒素（100 nmol/l）和氯化镉（100 μmol/l）显著抑制，表明N型钙通道在人和大鼠心脏交感神经元胞吐性去甲肾上腺素释放中起主要作用。地昔帕明（100 nmol/l）通过阻断神经元儿茶酚胺摄取（摄取1）增强了两种物种中电刺激诱发的去甲肾上腺素溢出。大鼠心脏的心肌缺血通过灌注流中断诱导，在人和大鼠心房组织中通过缺氧和无糖孵育模拟。大鼠心脏和人心房组织中缺血和缺氧诱导的去甲肾上腺素释放不受细胞外钙浓度变化的影响，甚至在去除钙并添加乙二醇双四乙酸（EGTA，1 mmol/l）后仍会发生。在两种物种中，ω-芋螺毒素（100 nmol/l）和氯化镉（100 μmol/l）均不影响大鼠心脏和心房以及人心房缺血诱导的去甲肾上腺素溢出。在人和大鼠心房组织中，在有氧存在的情况下阻断能量代谢（氰化物模型）导致去甲肾上腺素的地昔帕明敏感释放，并伴有DOPEG溢出，表明轴浆去甲肾上腺素浓度增加。这些数据提示人心脏中去甲肾上腺素释放存在双重机制。在常氧状态下，去甲肾上腺素释放受神经元钙内流调节，提示为胞吐性释放。然而，缺血诱导的去甲肾上腺素释放不依赖于钙，且被摄取1阻断所抑制，提示为非胞吐性释放机制。人心房组织中去甲肾上腺素释放的特征为缺血人心肌中交感神经元通过载体介导释放去甲肾上腺素提供了证据。
