MOLECULAR ORGANIZATION OF RENAL ORGANIC CATION TRANSPORT

有机阳离子包括大量具有重要药理作用的化合物。事实上，来自广泛临床类别的药物-包括抗组胺药、骨骼肌松弛药、抗心律失常药和β-肾上腺素能受体阻滞剂-都是有机阳离子(OCs)。肾脏在将这些化合物从体内清除出去的过程中起着关键作用，从而影响它们的临床有效性，并可能在排泄过程的水平上产生不良的相互作用。肾脏OC分泌的一般模型已经存在了近20年，但它不包括所涉及的过程的分子机制，因此缺乏建立阳离子药物肾脏分泌预测模型的基础。最近克隆的几个被认为在肾脏OC转运中发挥作用的候选转运体(OCT1、OCT2、OCTN1和OCTN2)使基于分子的分泌模型的发展成为可能，前提是获得了几个关键问题的答案：(1)这些转运体在肾脏中表达在哪里；(2)它们如何(从机制上)促进OC的分泌；以及(3)几个(当前)候选转运体中的每一个都处理什么底物？最后，(4)基于这些过程的测量特征，这些过程的整体行为能解释在近端小管观察到的分泌活动吗？为了回答这些问题，我们制定了一个实验计划，将检查以上列出的候选转运蛋白的特征，该方法包括比较从完整的肾小管获得的结果与使用单个克隆的转运蛋白获得的结果。后一种系统允许检查单一转运体的性质，而前者提供了唯一的手段来评估一系列过程的整合活动如何影响跨上皮细胞的净底物运动。克隆的转运体将包括四个转运体的人类同源基因，也包括每个过程的兔子同源基因。后一组观察将用于验证完整的小管系统的使用，我们将使用该系统来测试基于每个OC转运体的个体特征的阳离子药物分泌模型。这项研究将首次提供几个过程的综合观点，这些过程必须共同作用才能影响阳离子药物的肾脏分泌，从而为开发治疗上有用的肾脏药物分泌模型奠定必要的基础。

Organic cations include a vast collection of pharmacologically important compounds. Indeed, drugs from a wide array of clinical classes-including antihistamines, skeletal muscle relaxants, antiarrythmics, and beta- adrenoceptor blocking agents-are organic cations (Ocs). The kidney plays a critical role in clearing these compounds from the body, thereby influencing their clinical effectiveness and posing the potential for undesirable interactions at the level of the excretory process. A general model of renal OC secretion has been in place for almost 20 years, but it does not include the molecular mechanisms of the processes involved and, therefore lacks the basis upon which to build a predictive model of the renal secretion of cationic drugs. The recent cloning of several 'candidate transporters' believed to play a role in renal OC transport )OCT1, OCT2, OCTN1, and OCTN2) makes possible development of a molecularly-based secretory model, provided that answers to several critical questions are obtained: (1) Where are these transporters expressed in the kidney; (2) How (mechanistically) do they contribute to OC secretion; and (3) What substrates are handled by each of the several (current) candidate transporters? Finally, (4) Can the ensemble behavior of these processes, based upon their measured characteristics, account for the secretory activity observed in proximal tubules? To answer these questions we have developed an experimental plan that will examine the above listed characteristics of the candidate transporters The approach involves comparison of results obtained with intact renal tubules with those obtained using single cloned transport proteins. The latter system permits examination of the properties of single transporters, while the former provides the only means to assess how the integrated activity of a suite of processes influences net transepithelial substrate movement. The cloned transporters will include the human orthologs of the four transporters and, also, the rabbit orthologs of each process. The latter set of observation will be used to validate use of the intact tubule systems we will employ to test a model of cationic drug secretion based upon the individual characteristics of each OC transporter. This study will be the first to offer an integrated view of the several processes that must work together to effect renal secretion of cationic drugs and thereby establish the necessary base for developing a therapeutically useful model of renal drug secretion.