Noncompetitive inhibition of glycylsarcosine transport by quinapril in rabbit renal brush border membrane vesicles: effect on high-affinity peptide transporter.

Angiotensin converting enzyme (ACE) inhibitors are important therapeutic agents for treating patients with hypertension and cardiovascular diseases. Although most ACE inhibitors are cleared by the kidney via glomerular filtration and tubular secretion, little is known about their reabsorption potential. In particular, it is believed that while certain ACE inhibitors are transported by the intestinal peptide transporter (PepT1), these same compounds do not interact with the renal peptide transporter (PepT2). In the present study, we examined the interaction of quinapril with the high-affinity peptide transporter, PepT2. Studies were performed in rabbit renal brush border membrane vesicles in which the uptake of [14C]glycylsarcosine (GlySar), at low substrate concentrations, was examined in the absence and presence of quinapril (and other ACE inhibitors). We found that quinapril was capable of cis-inhibiting the uptake of GlySar and in a concentration-dependent manner. While the Ki for quinapril ( approximately 1 mM) was several-fold higher than the Km for GlySar ( approximately 160 microM), the interaction was unique in that inhibition of PepT2 was of a noncompetitive type. Overall, the data suggest that quinapril is a low-affinity inhibitor of the renal peptide transporter and that it binds to a site distinct from that of the GlySar binding site.