Russell J T, Martonosi A N
Biochim Biophys Acta. 1978 Dec 1;544(2):418-29. doi: 10.1016/0304-4165(78)90109-5.
The absorption spectrum of arsenazo III in media containing K+, Mg2+ and Ca2+ is sharply influenced by pH in the range of 7.5--5.0. The effect of pH is particularly pronounced in the wavelength range 532--602 nm due to the large pH dependence of the dissociation constant of Mg-arsenazo III complex. Therefore absorption changes at these wavelengths during muscle contraction cannot be used as reliable indicators of free ionized Ca2+ concentration in the cell. The effect of pH is less pronounced, but still noticeable at the wavelength pairs 575--650 or 660--685 nm. Multiple layers of muscle cells grown on polystyrene coils permit measurement of absorption changes of arsenazo III, introduced into the cells, by equilibration with 0.5 mM arsenazo III under routine culture conditions. The absorbance changes recorded at 660--685 nm are probably related to changes in intracellular free Ca2+ concentration.
在含有K⁺、Mg²⁺和Ca²⁺的介质中，偶氮胂III的吸收光谱在7.5 - 5.0的pH范围内会受到显著影响。由于Mg - 偶氮胂III络合物解离常数对pH的强烈依赖性，pH的影响在532 - 602 nm波长范围内尤为明显。因此，肌肉收缩过程中这些波长处的吸收变化不能用作细胞中游离离子化Ca²⁺浓度的可靠指标。pH的影响在575 - 650或660 - 685 nm波长对处不太明显，但仍然可以观察到。在聚苯乙烯螺旋上生长的多层肌肉细胞允许在常规培养条件下通过与0.5 mM偶氮胂III平衡来测量引入细胞中的偶氮胂III的吸收变化。在660 - 685 nm处记录的吸光度变化可能与细胞内游离Ca²⁺浓度的变化有关。
