Recently, we have demonstrated that the renal elimination of two drugs, disopyramide and pindolol, is stereoselective in humans. The overall goals of this continuation project are to examine further the clinical ramifications of stereoselective renal elimination and to explore the potential mechanisms that may be responsible for stereoselective renal elimination of drugs. In addition, the studies of stereoselectivity will be extended to examine the molecular features of transport of basic drugs in the kidney. The studies will be divided into 2 major sections: I. Stereoselective Reabsorption of Basic Drugs and II. Molecular Features of the Organic Cation Transport System. The studies of stereoselective reabsorption will involve both clinical and whole animal studies using a model compound, atenolol. Following the development of a stereospecific high performance liquid chromatographic analytical procedure for atenolol in biological fluids, the renal clearance of atenolol in normal human volunteers will be examined at various plasma concentrations to determine if active reabsorption occurs and if this reabsorption is stereoselective. The involvement of the basic amino acid transport system in the active reabsorption of atenolol in vivo will be specifically tested. Studies in isolated luminal membrane vesicles will be carried out to determine if basic drugs interact stereoselectively with the basic amino acid transport system. The studies elucidating the specific molecular features of the organic cation transport system will be carried out in isolated luminal and antiluminal membrane vesicles. The stereoselectivity of the organic cation transport system in the antiluminal membrane will be examined by studying inhibition of 3H-NMN uptake by various enantiomeric pairs. The functional groups essential for organic cation transport across both luminal and antiluminal membranes will be elucidated by using specific functional group modifying agents. Finally, we will synthesize molecules targeted to the organic cation transport system in the luminal membrane. These novel molecules will be tested for their ability to acylate tyrosine residues present on the transporter. The suitable compound will be used to specifically radiolabel the transporter. These studies will lead to a more sophisticated knowledge of drug transport by the kidneys.
