Energetics of Na+-dependent amino acid co-transport in Ehrlich ascites tumor cells.
Energetics of Na+-dependent amino acid co-transport in Ehrlich ascites tumor cells.
复制标题
艾利希腹水肿瘤细胞中 Na 依赖性氨基酸共转运的能量学。
DOI：
10.1016/0005-2736(87)90309-9
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Smith,TC
中科院分区：
文献类型：
--
作者：
Dawson,WD;Smith,TC
在2-氨基异丁酸的积聚过程中，艾氏腹水肿瘤细胞可从Na+电化学电位梯度(ΔμNa)中获得能量。细胞在含有0.25 mM 2-氨基异丁酸的不同[Na+](25-154 mM)的培养液中孵育，以建立氨基酸的最大稳定积累。用标准电生理技术测定膜电位(Vm)和细胞内Na+活性(a-Na)。在生理盐水([Na+]=15 4 mM)中，a Na为4.4±0.6 mm，胞浆内的表观Na+活度系数(γAPP)为0.17±0.0 2。在此条件下，Vm为−20.8±2.1 mV。由此推算出Δμ钠=9.9±0.8kJ/m ol。伴随2-氨基异丁酸积累的测定表明，能量需求(Δμ)为8.5±0.5kJ/mol.细胞外[Na+]的逐步减少可同时减少Na、Vm和2-氨基异丁酸的积累。然而，在所有测试条件下，来自Na+电化学电位梯度的可用能量超过了驱动2-氨基异丁酸摄取所需的能量。测定了2-氨基异丁酸对Vm的影响。在稳态细胞中加入10 mM白蛋白可在1min内引起膜去极化(静息Vm=−2 2.1±1.3 mV；加白蛋白Vm=−16.2±1.2 mV)。随后膜的复极化在10分钟内恢复到静止水平。在哇巴因(2 Mm)存在的情况下，复极化阶段被阻断。结果表明，Na+梯度提供的能量足以作为2-氨基异丁酸积累的来源。
The energy available from the Na+ electrochemical potential gradient (Δ μ Na) has been evaluated in Ehrlich ascites tumor cells during accumulation of 2-aminoisobutyric acid. Cells were incubated in media of varying [Na+](25–154 mM) in the presence of 0.25 mM 2-aminoisobutyric acid to establish maximum steady-state accumulation of the amino acid. Membrane potential (V m) and intracellular Na+ activity (a Na) were estimated using standard electrophysiological techniques. In physiological saline ([Na+]= 154 mM) a Na is 4.4±0.6 mM, giving an apparent Na+ activity coefficient (γ app) in the cytoplasm of 0.17±0.02. V m under these conditions is− 20.8±2.1 mV. From these values, Δ μ Na= 9.9±0.8 kJ/mol. Concomitant determinations of 2-aminoisobutyric acid (AIB) accumulation show an energy requirement (Δμ AIB) of 8.5±0.5 kJ/mol. Stepwise reductions in extracellular [Na+] give parallel reductions in a Na, V m and 2-aminoisobutyric acid accumulation. However, under all conditions tested the energy available from the Na+ electrochemical potential gradient exceeds that needed to drive 2-aminoisobutyric acid uptake. The effects of 2-aminoisobutyric acid on V m have also been determined. Addition of AIB (10 mM) to steady-state cells leads to membrane depolarization (resting V m=− 22.1±1.3 mV; plus AIB V m=− 16.2±1.2 mV) within 1 min. Subsequent repolarization of the membrane to resting levels occurs within 10 min. The repolarization phase is blocked in the presence of ouabain (2 mM). The results establish that the energy available from the Na+ gradient is sufficient to serve as a source for 2-aminoisobutyric acid accumulation.