p-AMINOHIPPURATE AND N-METHYLNICOTINAMIDE TRANSPORT IN DOG RENAL SLICES—AN EVALUATION OF THE COUNTER-TRANSPORT HYPOTHESIS

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

This study was undertaken to determine if counter-transport occurred in dog renal cortex slices in the transport of p-aminohippurate (PAH) and N-methylnicotinamide (NMN). Slices were preloaded in a medium containing a relatively high concentration of unlabeled PAH or NMN and then transferred to a second medium containing a low concentration of C¹⁴-labeled PAH or NMN. Preloading did not affect the rate of uptake when the slices were preloaded with moderate amounts of unlabeled PAH or NMN, whereas large amounts of PAH or NMN decreased the rate of uptake. To study the effect of preloading on the rate of runout, slices were preloaded with low concentrations of C¹⁴-labeled PAH or NMN which were released into medium containing high concentrations of unlabeled PAH or NMN. A significant increase in rate of runout was observed with PAH but no significant increase was observed with NMN. Since preloading increased transport only in one direction it was concluded that under the conditions of our experiments counter-transport does not occur in dog renal cortex slices in the transport of PAH and NMN. In addition, the results suggest that the mechanism involved in the uptake of PAH or NMN is different from the mechanism involved in the runout.