Regulation of the high‐affinity H/peptide cotransporter in renal LLC‐PK1 cells

Abstract

Di- and tripeptides and peptide mimetics such as β-lactam antibiotics are efficiently reabsorbed from the tubular lumen by a high-affinity peptide transporter. We have recently identified and characterized this H+-coupled high-affinity peptide transport system in the porcine proximal tubular cell line LLC-PK1. Here we describe for the first time the regulation of the renal high-affinity peptide cotransporter at the cellular level. Uptake of 5 μM 3H-D-Phe-L-Ala into LLC-PK1 cells was significantly increased by lowering [Ca2+]in and decreased by increasing [Ca2+]in. Moreover, it was shown that the [Ca2+]in effects on peptide transport activity were dependent on Ca2+ entry from the extracellular site (e.g., via a store-regulated capacitative Ca2+ influx). Protein kinase C (PKC) was found to transmit the effects of [Ca2+]in on peptide transport. Although we demonstrate by pHin measurements that the PKC inhibitor staurosporine did decrease the transmembrane H+ gradient and consequently should have reduced the driving force for peptide uptake, the only effect on transport kinetics of 3H-D-Phe-L-Ala observed was a significant decrease in Km from 22.7 ± 2.5 μM to 10.2 ± 1.9 μM with no change in maximal velocity. J. Cell. Physiol. 178:341–348, 1999. © 1999 Wiley-Liss, Inc.