ATTEMPTS TO LABEL THE RENAL CARRIER FOR ORGANIC BASES WITH DIBENAMINE

¹ Department of Pharmacology, State University of New York, Upstate Medical Center, Syracuse, New York

The technique of substrate protection was utilized to block the specific binding of Dibenamine. This enabled us to subsequently label the renal carrier of an organic base, N-methylnicotinamide. Renal cortex slices incubated with Dibenamine in the presence of various organic bases were protected against the inhibitory effects of Dibenamine. The extent of this protection depended upon the concentration of Dibenamine used. The inhibitory effects of Dibenamine could be prevented by the addition of sodium thiosulfate to the incubation medium; however, sodium thiosulfate was ineffective once Dibenamine had reacted with the slice. This confirms that the formation of the cyclic intermediate is necessary for the renal binding of Dibenamine. Experiments in which slices were exposed to 1) unlabeled Dibenamine or 2) unlabeled Dibenamine and tetraethylammonium or N-methylnicotinamide, then washed and exposed to Dibenamine-C¹⁴, washed a second time and finally fractioned into soluble, lipid and protein fractions, showed that only the protein fraction was protected by tetraethylammonium or N-methylnicotinamide. We conclude that the protein fraction contains a carrier-like protein. We have further concluded that the use of low concentrations of Dibenamine and short exposure times may facilitate the isolation of the carrier.