Neubauer S, Hamman B L, Perry S B, Bittl J A, Ingwall J S
Harvard Medical School NMR Laboratory, Boston, MA 02115.
Circ Res. 1988 Jul;63(1):1-15. doi: 10.1161/01.res.63.1.1.
Recovery of postischemic function may be limited by energy synthesis by mitochondria, energy transfer via the creatine kinase reaction, or energy utilization at myofibrils. To identify the limiting step, we defined the relations among oxygen consumption, creatine kinase reaction velocity and cardiac performance in myocardium reperfused following mild, moderate, and severe ischemia. Isolated isovolumic ferret hearts were perfused with Krebs-Henseleit buffer at 37 degrees C. After 30 minutes of control, hearts were made ischemic for 20, 40, or 60 minutes and reperfused for 40 minutes. During preischemia, cardiac performance (estimated as the rate-pressure product), was 14.8 x 10(3) mm Hg/min, oxygen consumption was 16.7 mumol/min/g dry weight, and creatine kinase reaction velocity measured by 31P-nuclear magnetic resonance saturation transfer was 12.7 mM/sec. For hearts reperfused after 20, 40, or 60 minutes of ischemia, rate-pressure product was 11.5, 6.5, and 1.1 x 10(3) mm Hg/min; oxygen consumption was 13.5, 14.2, and 6.9 mumol/min/g dry weight; and creatine kinase reaction velocity was 9.6, 5.0, and 2.0 mM/sec, respectively. Thus, with increasing severity of insult, creatine kinase reaction velocity decreased monotonically with performance (r = 0.99). Changes in creatine kinase reaction velocity were predicted from the creatine kinase rate equation (r = 0.99; predicted vs. measured velocity) and can therefore be explained by changes in substrate concentration. Oxygen consumption did not correlate with performance or creatine kinase velocity, consistent with abnormalities in mitochondrial energy production. In all cases, creatine kinase reaction velocity was an order of magnitude faster than the maximal rate of ATP synthesis estimated by oxygen consumption. We conclude that, in postischemic myocardium, creatine kinase reaction velocity decreases in proportion to performance, but high-energy phosphate transfer does not limit availability of high-energy phosphate for contraction.
缺血后功能的恢复可能受到线粒体能量合成、通过肌酸激酶反应的能量转移或肌原纤维处能量利用的限制。为了确定限制步骤，我们定义了轻度、中度和重度缺血后再灌注心肌中氧消耗、肌酸激酶反应速度和心脏功能之间的关系。将离体等容雪貂心脏在37℃下用克雷布斯 - 亨塞尔特缓冲液灌注。在对照30分钟后，使心脏缺血20、40或60分钟，然后再灌注40分钟。在缺血前，心脏功能（以速率 - 压力乘积估计）为14.8×10³mmHg/min，氧消耗为16.7μmol/min/g干重，通过³¹P - 核磁共振饱和转移测量的肌酸激酶反应速度为12.7mM/sec。对于缺血20、40或60分钟后再灌注的心脏，速率 - 压力乘积分别为11.5、6.5和1.1×10³mmHg/min；氧消耗分别为13.5、14.2和6.9μmol/min/g干重；肌酸激酶反应速度分别为9.6、5.0和2.0mM/sec。因此，随着损伤严重程度的增加，肌酸激酶反应速度随心脏功能单调下降（r = 0.99）。肌酸激酶反应速度的变化可由肌酸激酶速率方程预测（r = 0.99；预测速度与测量速度），因此可以用底物浓度的变化来解释。氧消耗与心脏功能或肌酸激酶速度无关，这与线粒体能量产生异常一致。在所有情况下，肌酸激酶反应速度比通过氧消耗估计的ATP合成最大速率快一个数量级。我们得出结论，在缺血后心肌中，肌酸激酶反应速度与心脏功能成比例下降，但高能磷酸转移并不限制用于收缩的高能磷酸的可用性。
