Tian R, Christe M E, Spindler M, Hopkins J C, Halow J M, Camacho S A, Ingwall J S
NMR Laboratory for Physiological Chemistry, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
J Clin Invest. 1997 Feb 15;99(4):745-51. doi: 10.1172/JCI119220.
Sarcomere relaxation depends on dissociation of actin and myosin, which is regulated by a number of factors, including intracellular [MgATP] as well as MgATP hydrolysis products [MgADP] and inorganic phosphate [Pi], pHi, and cytosolic calcium concentration ([Ca2+]c). To distinguish the contribution of MgADP from the other regulators in the development of diastolic dysfunction, we used a strategy to increase free [MgADP] without changing [MgATP], [Pi], or pHi. This was achieved by applying a low dose of iodoacetamide to selectively inhibit the creatine kinase activity in isolated perfused rat hearts. [MgATP], [MgADP], [Pi], and [H+] were determined using 31P NMR spectroscopy. The [Ca2+]c and the glycolytic rate were also measured. We observed an approximately threefold increase in left ventricular end diastolic pressure (LVEDP) and 38% increase in the time constant of pressure decay (P < 0.05) in these hearts, indicating a significant impairment of diastolic function. The increase in LVEDP was closely related to the increase in free [MgADP]. Rate of glycolysis was not changed, and [Ca2+]c increased by 16%, which cannot explain the severity of diastolic dysfunction. Thus, our data indicate that MgADP contributes significantly to diastolic dysfunction, possibly by slowing the rate of cross-bridge cycling.
肌节舒张依赖于肌动蛋白和肌球蛋白的解离，这一过程受多种因素调控，包括细胞内[MgATP]以及MgATP水解产物[MgADP]和无机磷酸[Pi]、细胞内pH值（pHi）和胞质钙浓度（[Ca2+]c）。为了区分MgADP与其他调节因子在舒张功能障碍发展中的作用，我们采用了一种策略来增加游离[MgADP]，同时不改变[MgATP]、[Pi]或pHi。这是通过应用低剂量的碘乙酰胺来选择性抑制离体灌注大鼠心脏中的肌酸激酶活性实现的。使用31P核磁共振波谱法测定[MgATP]、[MgADP]、[Pi]和[H+]。还测量了[Ca2+]c和糖酵解速率。我们观察到这些心脏的左心室舒张末期压力（LVEDP）大约增加了三倍，压力衰减时间常数增加了38%（P < 0.05），表明舒张功能有显著损害。LVEDP的增加与游离[MgADP]的增加密切相关。糖酵解速率没有变化，[Ca2+]c增加了16%，这无法解释舒张功能障碍的严重程度。因此，我们的数据表明MgADP可能通过减慢横桥循环速率对舒张功能障碍有显著影响。
