Dantzig A H, Bergin L
Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN 46285.
Biochim Biophys Acta. 1990 Sep 7;1027(3):211-7. doi: 10.1016/0005-2736(90)90309-c.
The transport of the orally absorbed cephalosporin, cephalexin, was examined in the human epithelial cell line, Caco-2 that possesses intestinal enterocyte-like properties when cultured. In sodium-free buffer, the cells accumulated 1 mM D-[9-14C]cephalexin against a concentration gradient and obtained a distribution ratio of 3.5 within 180 min. Drug uptake was maximal when the extracellular pH was 6.0. Uptake was reduced by metabolic inhibitors and by protonophores indicating that uptake was energy- and proton-dependent. Kinetic analysis of the concentration dependence of the rate of cephalexin uptake showed that a non-saturable component (Kd of 0.18 +/- 0.01 nmol/min per mg protein per mM) and a transport system with a Km of 7.5 +/- 2.8 mM and a Vmax of 6.5 +/- 0.9 nmol/min per mg protein were responsible for drug uptake. Uptake was competitively inhibited by dipeptides. The transport carrier exhibited stereospecificity for the L-isomer of cephalexin. Drug uptake was not affected by the presence of amino acids, organic anions, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid or 4,4'-diisothiocyano-2,2'-disulfonic stilbene. Therefore, Caco-2 cells take up cephalexin by a proton-dependent dipeptide transport carrier that closely resembles the transporter present in the intestine. Caco-2 cells represent a cellular model for future studies of the dipeptide transporter.
在人上皮细胞系Caco-2中研究了口服吸收的头孢菌素头孢氨苄的转运情况，该细胞系在培养时具有肠上皮细胞样特性。在无钠缓冲液中，细胞逆浓度梯度积累1 mM D-[9-¹⁴C]头孢氨苄，并在180分钟内获得3.5的分布比。当细胞外pH为6.0时，药物摄取量最大。代谢抑制剂和质子载体可降低摄取量，表明摄取是能量和质子依赖性的。头孢氨苄摄取速率的浓度依赖性动力学分析表明，一个非饱和成分（每毫克蛋白质每毫摩尔的Kd为0.18±0.01 nmol/min）和一个Km为7.5±2.8 mM、Vmax为每毫克蛋白质6.5±0.9 nmol/min的转运系统负责药物摄取。摄取受到二肽的竞争性抑制。转运载体对头孢氨苄的L-异构体表现出立体特异性。氨基酸、有机阴离子、4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸或4,4'-二异硫氰基-2,2'-二磺酸芪的存在不影响药物摄取。因此，Caco-2细胞通过一种质子依赖性二肽转运载体摄取头孢氨苄，该载体与肠道中的转运体非常相似。Caco-2细胞代表了未来二肽转运体研究的细胞模型。
