Buist R J, Deslauriers R, Saunders J K, Mainwood G W
Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ont.
Can J Physiol Pharmacol. 1991 Nov;69(11):1663-9. doi: 10.1139/y91-247.
23Na nuclear magnetic resonance spectroscopy (NMR) is increasingly being used to study Na+ gradients and fluxes in biological tissues. However, the quantitative aspects of 23Na NMR applied to living systems remain controversial. This paper compares sodium concentrations determined by 23Na NMR in intact rat hindlimb (n = 8) and excised rat gastrocnemius muscle (n = 4) with those obtained by flame photometric methods. In both types of samples, 90% of the sodium measured by flame photometry was found to be NMR-visible. This is much higher than previously reported values. The NMR measurements for intact hindlimb correlated linearly with the flame photometric measurements, implying that one pool of sodium, predominantly extracellular, is 100% visible. From measurements on excised muscle, in which extracellular space is more clearly defined, the NMR visibility of intracellular Na+ was calculated to be 70%, assuming an extracellular space of 12% of the total tissue water volume and an extracellular NMR visibility of 100%. 23Na transverse relaxation measurements were carried out using a Hahn spin echo on both intact hindlimb (n = 1) and excised muscle (n = 2) samples. These showed relaxation curves that could each be described adequately using two relaxation times. The rapidly relaxing component showed a T2 value of 3-4 ms and the slowly relaxing component a T2 of 21-37 ms. A spin lattice relaxation (T1) measurement on intact hindlimb yielded a value of 51 ms. These relatively long relaxation times show that the quadrupolar relaxation effect of Na+ complexing to large macromolecules or being otherwise motionally restricted is relatively weak. This is consistent with the high NMR visibilities reported here.
23Na核磁共振光谱法（NMR）越来越多地用于研究生物组织中的Na+梯度和通量。然而，应用于活体系统的23Na NMR的定量方面仍存在争议。本文将通过23Na NMR测定的完整大鼠后肢（n = 8）和切除的大鼠腓肠肌（n = 4）中的钠浓度与通过火焰光度法获得的钠浓度进行了比较。在这两种类型的样品中，发现通过火焰光度法测量的钠中有90%是NMR可见的。这比先前报道的值要高得多。完整后肢的NMR测量值与火焰光度测量值呈线性相关，这意味着主要位于细胞外的一组钠是100%可见的。根据对切除肌肉的测量（其中细胞外空间更明确），假设细胞外空间占总组织水体积的12%且细胞外NMR可见度为100%，计算出细胞内Na+的NMR可见度为70%。使用哈恩自旋回波对完整后肢（n = 1）和切除肌肉（n = 2）样品进行了23Na横向弛豫测量。这些测量显示弛豫曲线，每条曲线都可以用两个弛豫时间来充分描述。快速弛豫成分的T2值为3 - 4毫秒，缓慢弛豫成分的T2为21 - 37毫秒。对完整后肢进行的自旋晶格弛豫（T1）测量得出的值为51毫秒。这些相对较长的弛豫时间表明，Na+与大分子络合或以其他方式受到运动限制的四极弛豫效应相对较弱。这与本文报道的高NMR可见度一致。
