Bowers-Komro D M, McCormick D B
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
J Nutr. 1991 Jan;121(1):57-64. doi: 10.1093/jn/121.1.57.
Isolated kidney cells accumulated L[1-14C]ascorbic acid in a time-dependent manner and reached a steady state after 15 min at 37 degrees C. Initial velocity for uptake was over 300 pmol/mg protein per min when cells were separated from the bathing solution using a density gradient established during centrifugation. The uptake process was saturable with an apparent concentration at half maximal uptake of 36 mumols/L. Ascorbate uptake was reduced by metabolic inhibitors and was temperature dependent. Although ascorbic acid is an acid anion at pH 7.4, uptake did not appear to be inhibited by other acid anions such as p-aminohippurate and probenecid; however, involvement of the ion gradient established by Na+, H(+)-adenosine triphosphatase could not be confirmed. Replacing the sodium ion with other monovalent ions reduced the accumulation of ascorbate significantly. Isoascorbic and dehydroascorbic acids inhibited ascorbate uptake (34 and 13 mmol/L, respectively), whereas high concentrations of glucose showed some stimulation. These findings indicated that ascorbic acid is reabsorbed by the kidney in a sodium-dependent active transport process that is not common to other acid anions and has some specificity for the ascorbic acid structure.
分离的肾细胞以时间依赖性方式积累L-[1-¹⁴C]抗坏血酸，并在37℃下15分钟后达到稳态。当使用离心过程中建立的密度梯度将细胞与浴液分离时，摄取的初始速度超过300 pmol/mg蛋白质每分钟。摄取过程是可饱和的，半最大摄取时的表观浓度为36 μmol/L。抗坏血酸摄取受到代谢抑制剂的抑制，并且依赖于温度。尽管抗坏血酸在pH 7.4时是一种酸性阴离子，但摄取似乎不受其他酸性阴离子如对氨基马尿酸和丙磺舒的抑制；然而，由Na⁺，H⁺-腺苷三磷酸酶建立的离子梯度的参与无法得到证实。用其他单价离子取代钠离子会显著降低抗坏血酸的积累。异抗坏血酸和脱氢抗坏血酸抑制抗坏血酸摄取（分别为34和13 mmol/L），而高浓度的葡萄糖则表现出一定的刺激作用。这些发现表明，抗坏血酸在肾脏中通过一种钠依赖性主动转运过程被重吸收，这种过程对其他酸性阴离子并不常见，并且对抗坏血酸结构具有一定的特异性。
