Goldhaber J I, Kim K H, Natterson P D, Lawrence T, Yang P, Weiss J N
Division of Cardiology, School of Medicine, University of California, Los Angeles 90095, USA.
Am J Physiol. 1996 Oct;271(4 Pt 2):H1449-55. doi: 10.1152/ajpheart.1996.271.4.H1449.
The mechanism of the acute negative inotropic effect of tumor necrosis factor-alpha (TNF-alpha) was studied in enzymatically isolated adult rabbit ventricular myocytes. In cells loaded with fura 2 acetoxymethyl ester (AM) and paced intermittently at 0.2 Hz, TNF-alpha at doses < or = 10,000 U/ml caused a significant reduction in active cell shortening at 20 min, without reducing the amplitude of the accompanying intracellular Ca2+ concentration ([Ca2+]i) transient. Similar results were obtained in cells loaded with indo 1-AM and paced continuously at 0.2 Hz during exposure to TNF-alpha (10,000 U/ml). The effect of TNF-alpha on cell shortening could be prevented by the nitric oxide (NO) synthase blocker NG-nitro-L-arginine methyl ester (L-NAME) but not its inactive enantiomer NG-nitro-D-arginine methyl ester (D-NAME). The NO scavenger hemoglobin also attenuated the effects of TNF-alpha. TNF-alpha also caused a significant increase in diastolic cell length without any change in diastolic [Ca2+]i. The effect on cell length was prevented by L-NAME but not D-NAME. In cells loaded with the pH indicator seminaphthorhodafluor-AM, TNF-alpha did not alter pH sufficiently to account for the negative inotropic effect. These data suggest that high doses of TNF-alpha can acutely induce NO synthesis in isolated myocytes and reduce contractility by decreasing myofilament [Ca2+]i responsiveness. The mechanism of this altered myofilament [Ca2+]i response is unknown but does not appear to be pH mediated.
在酶解分离的成年兔心室肌细胞中研究了肿瘤坏死因子-α（TNF-α）急性负性肌力作用的机制。在用乙酰氧甲基酯（AM）形式的fura 2加载的细胞中，以0.2 Hz的频率间歇性起搏，剂量≤10,000 U/ml的TNF-α在20分钟时可导致活跃的细胞缩短显著减少，而不降低伴随的细胞内Ca2+浓度（[Ca2+]i）瞬变的幅度。在用indo 1-AM加载的细胞中，在暴露于TNF-α（10,000 U/ml）期间以0.2 Hz的频率持续起搏，也得到了类似的结果。TNF-α对细胞缩短的作用可被一氧化氮（NO）合酶阻滞剂NG-硝基-L-精氨酸甲酯（L-NAME）阻断，但不能被其无活性的对映体NG-硝基-D-精氨酸甲酯（D-NAME）阻断。NO清除剂血红蛋白也减弱了TNF-α的作用。TNF-α还导致舒张期细胞长度显著增加，而舒张期[Ca2+]i无任何变化。对细胞长度的作用可被L-NAME阻断，但不能被D-NAME阻断。在用pH指示剂半萘荧光素-AM加载的细胞中，TNF-α没有使pH改变到足以解释负性肌力作用的程度。这些数据表明，高剂量的TNF-α可在分离的心肌细胞中急性诱导NO合成，并通过降低肌丝对[Ca2+]i的反应性来降低收缩性。这种改变的肌丝对[Ca2+]i反应的机制尚不清楚，但似乎不是由pH介导的。
