Intracellular pH-regulating mechanism of the squid axon. Relation between the external Na+ and HCO-3 dependences.
Intracellular pH-regulating mechanism of the squid axon. Relation between the external Na+ and HCO-3 dependences.
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DOI：
10.1085/jgp.85.3.325
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发表时间：
1985-03
影响因子：
3.8
通讯作者：
Boron, W F
中科院分区：
文献类型：
--
作者：
Boron, W F
鱿鱼轴突的细胞内pH值调节机制进行了检查，其依赖于外部Na+和HCO 3-的浓度，总是在外部pH值（pH值）为8.0。将具有约7.4的初始细胞内pH（pHi）的轴突用含有400 mM Cl-且不含Na+的pH 6.5的溶液进行内部透析。在pHi下降到约6.6后，停止透析，从而将pHi的控制权返回到轴突。随着外部Na+和HCO-3的存在，细胞内的pH值（pHi）增加，因为pH调节系统的活动。酸挤出速率（即，H+的当量流出，JH）是pHi恢复速率、细胞内缓冲能力和体积与表面比的乘积。在[Na+]o的三个固定水平：425、212和106 mM下检查JH的[HCO 3-]o依赖性。在所有三种情况下，表观Jmax约为19 pmol X cm-2 X s-1。然而，表观Km（HCO 3-）与[Na+]o近似成反比，随着[Na+]o从425 mM降低到212 mM再到106 mM，表观Km（HCO 3-）从2.6 mM升高到5.4 mM再到9.7 mM。在三个固定水平的[HCO 3-]o：12，6，和3 mM下，同样检查了JH的[Na+]o依赖性。Jmax值与第一系列实验中的值没有显著差异。然而，表观Km（Na+）与[HCO 3-]o近似负相关，当[HCO 3-]o从12 mM降低到6 mM到3 mM时，表观Km（Na+）从71 mM升高到174 mM再到261 mM。这些结果与酸挤出的离子对模型的预测一致，该模型具有外部Na+和CO 3 =结合形成离子对NaCO 3-，然后交换内部Cl-。当将JH数据重新绘制为[NaCO 3- ]o的函数时，来自所有六组实验的数据沿着相同的Michaelis-Menten曲线下降，表观Km（NaCO 3-）为80 μ M。Na+和CO 3 =的有序和随机结合不能被排除作为可能的模型，但限制在允许的速率常数组合。
The intracellular pH-regulating mechanism of the squid axon was examined for its dependence on the concentrations of external Na+ and HCO3-, always at an external pH (pHo) of 8.0. Axons having an initial intracellular pH (pHi) of approximately 7.4 were internally dialyzed with a solution of pH 6.5 that contained 400 mM Cl- and no Na+. After pHi had fallen to approximately 6.6, dialysis was halted, thereby returning control of pHi to the axon. With external Na+ and HCO-3 present, intracellular pH (pHi) increased because of the activity of the pHi-regulating system. The acid extrusion rate (i.e., equivalent efflux of H+, JH) is the product of the pHi recovery rate, intracellular buffering power, and the volume-to-surface ratio. The [HCO3-]o dependence of JH was examined at three fixed levels of [Na+]o: 425, 212, and 106 mM. In all three cases, the apparent Jmax was approximately 19 pmol X cm-2 X s-1. However, the apparent Km (HCO3-) was approximately inversely proportional to [Na+]o, rising from 2.6 to 5.4 to 9.7 mM as [Na+]o was lowered from 425 to 212 to 106 mM, respectively. The [Na+]o dependence of JH was similarly examined at three fixed levels of [HCO3-]o: 12, 6, and 3 mM. The Jmax values did not vary significantly from those in the first series of experiments. The apparent Km (Na+), however, was approximately inversely related to [HCO3-]o, rising from 71 to 174 to 261 mM as [HCO3-]o was lowered from 12 to 6 to 3 mM, respectively. These results agree with the predictions of the ion-pair model of acid extrusion, which has external Na+ and CO3= combining to form the ion pair NaCO3-, which then exchanges for internal Cl-. When the JH data are replotted as a function of [NaCO3- ]o, data from all six groups of experiments fall along the same Michaelis-Menten curve, with an apparent Km (NaCO3-) of 80 microM. The ordered and random binding of Na+ and CO3= cannot be ruled out as possible models, but are restricted in allowable combinations of rate constants.