Fishbein W N, Davis J I, Foellmer J W, Casey M R
Division of Biochemistry, Armed Forces Institute of Pathology, Washington, D.C. 20306.
Biochem Med Metab Biol. 1988 Jun;39(3):351-9. doi: 10.1016/0885-4505(88)90095-3.
We have applied a lactate efflux assay to human red cells at two temperatures and with initial lactic acid loads up to 8 mM, metabolically generated. Efflux was about 1.5 times faster at external pH of 8.5 than at 7.5; the latter was the standard pH used thereafter. Multiple lactate loads in a single blood specimen demonstrated clear evidence of saturation kinetics at both pH levels, since the efflux rate did not increase proportionally with the lactate load. Best-fitting rectangular hyperboles were determined for 129-131 assays from 43 volunteers at 20 degrees and 30 degrees. In most cases high and low lactate loads permitted a two-point evaluation of saturation kinetics, and a positive indication was obtained in 88 of 89 tests. The apparent efflux Km and Vm values may be influenced by pH as well as by lactate levels and cannot be taken as rigorous, although they agree reasonably well with literature data on influx and exchange velocities. The data displayed a Hill constant of 1, a 30 degrees/20 degrees velocity ratio of 2.7, and no significant clustering by sex or age. A single assay with initial lactate level above 5 mM at 30 degrees should be sufficient to identify cases with a defective transporter, using the 95% tolerance limits developed in this report.
我们在两个温度下，对初始乳酸负荷高达8 mM（代谢产生）的人红细胞应用了乳酸外流测定法。在外部pH值为8.5时，外流速度比pH值为7.5时快约1.5倍；此后使用后者作为标准pH值。在单个血液样本中进行多次乳酸负荷实验，结果表明在两种pH水平下均有明显的饱和动力学证据，因为外流速率并不随乳酸负荷成比例增加。对来自43名志愿者的129 - 131次测定在20℃和30℃下进行了最佳拟合的矩形双曲线测定。在大多数情况下，高乳酸负荷和低乳酸负荷允许对饱和动力学进行两点评估，在89次测试中有88次得到了阳性结果。表观外流Km和Vm值可能受pH值以及乳酸水平的影响，不能被视为严格准确的值，尽管它们与关于流入和交换速度的文献数据相当吻合。数据显示希尔常数为1, 30℃与20℃时的速度比为2.7，并且没有按性别或年龄进行明显聚类。使用本报告中制定的95%耐受限度，在30℃下对初始乳酸水平高于5 mM进行单次测定，应该足以识别转运体缺陷的病例。
