原位大鼠心脏的生物能量学与氧消耗控制

Bioenergetics and control of oxygen consumption in the in situ rat heart.

作者信息

Headrick J P, Dobson G P, Williams J P, McKirdy J C, Jordan L, Willis R J

机构信息

Department of Molecular Sciences, James Cook University of North Queensland, Townsville, Australia.

出版信息

Am J Physiol. 1994 Sep;267(3 Pt 2):H1074-84. doi: 10.1152/ajpheart.1994.267.3.H1074.

DOI:10.1152/ajpheart.1994.267.3.H1074

PMID:8092272

Abstract

Control of respiration by products of ATP hydrolysis was examined in the in situ rat heart using a purpose-built nuclear magnetic resonance (NMR) coil. The in situ ratio of phosphocreatine to ATP concentrations ([PCr]/[ATP]) was 2.30 +/- 0.05, free Mg2+ concentration ([Mg2+]) was 0.57 mM, and cytosolic pH was 7.35 +/- 0.03 (n = 7). Basal inorganic phosphate concentration ([Pi]) was below NMR detection but was estimated to be 0.83 mM. The [ATP]/[ADP] [Pi] ratio, free ADP concentration ([ADP]), and free energy of ATP hydrolyses (delta GATP) were calculated to be 700,000 +/- 78,000 M-1, 18 +/- 3 microM, and -63.93 +/- 0.33 kJ/mol in situ, respectively (n = 7). In contrast, in the Langendorff perfused rat heart [ATP]/[ADP] [Pi] was only 76,140 +/- 12,830 M-1, [ADP] was 65 +/- 9 microM, and delta GATP was -59.92 +/- 0.48 kJ/mol (n = 7), all indicative of a lower energy state in vitro. Epinephrine infusion in situ (0.9 microgram.min-1.kg-1) increased the rate-pressure product 2.05-fold. During stimulation [ATP] was stable at 97 +/- 3% signal intensity, [PCr] declined by 25%, and [Pi] increased to 1.83 mM. Cytosolic pH was 7.27 +/- 0.01 and [Mg2+] was 0.64 +/- 0.05 mM. [PCr]/[ATP] declined to 1.83 +/- 0.13, and [ATP]/[ADP] [Pi] fell to 108,000 +/- 15,000 M-1. delta GATP only fell marginally to -59.56 +/- 0.49 kJ/mol. Free [ADP] increased threefold to 55 +/- 10 microM. Infusion of 2.8 +/- 0.5 microgram.min-1.kg-1 epinephrine increased the rate-pressure product 2.7-fold, further reduced [ATP]/[ADP] [Pi] (5% of basal), and elevated [ADP] more than fourfold without changing [ATP]. We conclude that the in situ heart is highly energetic compared with isolated perfused hearts and operates at a different metabolic "set-point." Because free [ADP] and [Pi] in situ approximate apparent Michaelis constants for mitochondrial respiration in vitro and increase with increased cardiac work, we conclude that each fulfills the criteria for the kinetic control of O2 consumption in the in situ rat myocardium.

摘要

利用特制的核磁共振（NMR）线圈，在原位大鼠心脏中研究了ATP水解产物对呼吸的控制。原位磷酸肌酸与ATP浓度的比值（[PCr]/[ATP]）为2.30±0.05，游离镁离子浓度（[Mg2+]）为0.57 mM，胞质pH值为7.35±0.03（n = 7）。基础无机磷酸盐浓度（[Pi]）低于NMR检测水平，但估计为0.83 mM。原位[ATP]/[ADP][Pi]比值、游离ADP浓度（[ADP]）和ATP水解自由能（δGATP）经计算分别为700,000±78,000 M-1、18±3 μM和-63.93±0.33 kJ/mol（n = 7）。相比之下，在Langendorff灌注的大鼠心脏中，[ATP]/[ADP][Pi]仅为76,140±12,830 M-1，[ADP]为65±9 μM，δGATP为-59.92±0.48 kJ/mol（n = 7），所有这些都表明体外能量状态较低。原位注射肾上腺素（0.9 μg·min-1·kg-1）使速率-压力乘积增加2.05倍。刺激期间，[ATP]在信号强度97±3%时保持稳定，[PCr]下降25%，[Pi]增加至1.83 mM。胞质pH值为7.27±0.01，[Mg2+]为0.64±0.05 mM。[PCr]/[ATP]降至1.83±0.13，[ATP]/[ADP][Pi]降至108,000±15,000 M-1。δGATP仅略微降至-59.56±0.49 kJ/mol。游离[ADP]增加三倍至55±10 μM。注射2.8±0.5 μg·min-1·kg-1肾上腺素使速率-压力乘积增加2.7倍，进一步降低[ATP]/[ADP][Pi]（至基础值的5%），且[ADP]升高超过四倍而[ATP]不变。我们得出结论，与离体灌注心脏相比，原位心脏能量水平很高，且在不同的代谢“设定点”运作。由于原位游离[ADP]和[Pi]接近体外线粒体呼吸的表观米氏常数，且随心脏工作增加而升高，我们得出结论，二者均符合原位大鼠心肌中氧气消耗动力学控制的标准。