Nishino H, Schiller R M, Parnes J R, Isselbacher K J
Proc Natl Acad Sci U S A. 1978 May;75(5):2329-32. doi: 10.1073/pnas.75.5.2329.
The uptake of alpha-amino[(3)H]isobutyric acid (AIB) was studied in membrane vesicles from mouse fibroblasts transformed by simian virus 40 to examine the features of the Na(+)-stimulated and Na(+)-dependent AIB transport process. The simultaneous addition of NaCl and AIB to these vesicles produced a transient accumulation, or "overshoot," of amino acid 3-4 times the equilibrium value. Both the initial rate of uptake and the rate of fall of intravesicular AIB after maximal accumulation were sensitive to the temperature of incubation. The overshoot of AIB uptake was enhanced with Na(+) salts of highly permeant lipophilic anions, such as SCN(-) and NO(3) (-), and was decreased by the addition of SO(4) (2-), a relatively impermeant ion. Gramicidin D, which enhances the membrane conductance of Na(+) electrogenically, decreased the overshoot, while a potassium diffusion potential, induced by valinomycin (in K(+)-preloaded membrane vesicles), produced a Na(+)-dependent overshoot of AIB uptake. When vesicles were preincubated with both Na(+) and AIB, followed by the generation of an interior negative membrane potential (by the addition of SCN(-)), an overshoot of AIB uptake resulted. However, this did not occur in the absence of Na(+). It is concluded that, apart from its role in the generation of a transmembrane electrochemical potential, Na(+) is essential for the overshoot of AIB uptake.
研究了用猿猴病毒40转化的小鼠成纤维细胞膜囊泡中α-氨基[³H]异丁酸（AIB）的摄取情况，以检验Na⁺刺激的和Na⁺依赖性AIB转运过程的特征。向这些膜囊泡中同时加入NaCl和AIB会产生氨基酸的瞬时积累，即“过冲”，其积累量是平衡值的3至4倍。摄取的初始速率以及最大积累后囊泡内AIB的下降速率均对孵育温度敏感。高渗透性亲脂性阴离子（如SCN⁻和NO₃⁻）的钠盐会增强AIB摄取的过冲，而加入相对低渗透性的离子SO₄²⁻则会使其降低。短杆菌肽D可增强Na⁺的膜电导，它会降低过冲，而缬氨霉素（在预加载K⁺的膜囊泡中）诱导的钾扩散电位会产生Na⁺依赖性的AIB摄取过冲。当膜囊泡先用Na⁺和AIB预孵育，然后通过加入SCN⁻产生内部负膜电位时，会导致AIB摄取过冲。然而，在没有Na⁺时不会发生这种情况。得出的结论是，除了其在跨膜电化学电位产生中的作用外，Na⁺对于AIB摄取的过冲是必不可少的。
