Schwerdt G, Freudinger R, Silbernagl S, Gekle M
Physiologisches Institut, Universität Würzburg, Germany.
Toxicology. 1998 Nov 16;131(2-3):193-202. doi: 10.1016/s0300-483x(98)00135-8.
Uptake of ochratoxin A (OTA) across the apical cell membrane of collecting duct cells is the first step in reabsorption and partly mediated by proton-dipeptide cotransport. As the remaining part of apical OTA uptake remained unclear, we studied the characteristics of apical uptake of tritium-labelled OTA (3H-OTA) in MDCK-C11 cells in detail. Uptake of 3H-OTA was pH- and temperature-dependent and led to intracellular accumulation of OTA. Lowering pH led to an increase and lowering temperature (4 degrees C) to a decrease of OTA uptake. Besides dipeptides, the beta-lactam antibiotics cephalexin and ceftibuten inhibited the 3H-OTA uptake also confirming the role of the proton dipeptide cotransporter. In addition, substrates of organic anion transporter, taurocholate and methotrexate, inhibited 3H-OTA uptake in part. Aspartylphenylalanine methyl ester (aspartame) had no inhibitory effect on 3H-OTA uptake. Uptake of OTA was not dependent on sodium. Sixty minutes of preincubation with phorbol 12-myristate 13-acetate (PMA) led to increased apical uptake of OTA. The PMA effects were inhibited by ethylisopropylamilorid (EIPA). We conclude that apical uptake of OTA occurs by Na+-independent transport. One part of the uptake is mediated by proton-dipeptide cotransport (30%, dipeptide-inhibitable), by organic anion transporter (20%, taurocholate-inhibitable) and by diffusion (20%, responsible for uptake at 4 degrees C). The remaining part occurs by as yet unidentified but pH-dependent transport mechanisms. An acidic urine in distal parts of the nephron provides thus the main risk for OTA uptake leading to its reabsorption and consequently alkalinisation of the urine should help to prevent this reabsorption.
赭曲霉毒素A（OTA）跨集合管细胞顶端细胞膜的摄取是重吸收的第一步，部分由质子 - 二肽共转运介导。由于顶端OTA摄取的其余部分尚不清楚，我们详细研究了MDCK - C11细胞中氚标记的OTA（3H - OTA）顶端摄取的特性。3H - OTA的摄取是pH和温度依赖性的，并导致OTA在细胞内积累。降低pH导致OTA摄取增加，降低温度（4℃）导致OTA摄取减少。除二肽外，β-内酰胺抗生素头孢氨苄和头孢布烯也抑制3H - OTA摄取，这也证实了质子二肽共转运体的作用。此外，有机阴离子转运体的底物牛磺胆酸盐和甲氨蝶呤部分抑制3H - OTA摄取。天冬氨酰苯丙氨酸甲酯（阿斯巴甜）对3H - OTA摄取没有抑制作用。OTA的摄取不依赖于钠。用佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）预孵育60分钟导致OTA顶端摄取增加。PMA的作用被乙基异丙基amilorid（EIPA）抑制。我们得出结论，OTA的顶端摄取通过不依赖于Na + 的转运发生。摄取的一部分由质子 - 二肽共转运介导（30％，可被二肽抑制），由有机阴离子转运体介导（20％，可被牛磺胆酸盐抑制）和通过扩散介导（20％，负责4℃时的摄取）。其余部分通过尚未确定但pH依赖性的转运机制发生。因此，肾单位远端的酸性尿液为OTA摄取导致其重吸收提供了主要风险，因此尿液碱化应有助于防止这种重吸收。
