A new use of the biosensor Di-C₃-(3) to measure dipeptide transport across the apical membrane of the renal proximal tubule

PEPT1 and PEPT2 are H+-dependent cotransporters found in the kidney. They are important for the reabsorption of small peptides and are also capable of transporting a broad range of peptidomimetic drugs. Due to the electrogenic nature of these carriers, transport of individual substrates should be accompanied by a positive change in the membrane potential difference (pd). The aim of this study was to investigate a novel use for the potential sensitive fluorescent dye 3,30-dipropylthiacarbocyanine iodide [DiS-C₃-(3)] as a biosensor for dipeptide transport across the renal proximal tubule apical membrane. Brush border (BBMV) and outer medulla (OMMV) membrane vesicles were isolated from male Wistar rats using standard techniques. Fluorescence changes were measured when extracellular media at pH 6.6 containing 0-3 mM L-glycyl-L-glutamine (gly-gln) was added to a cuvette containing vesicles pre-equilibrated at pH 7.4 and 7.5 μM DiS-C₃-(3). Data presented are means ± SE of n = 6. A positive change in fluorescence occurred upon gly-gln addition reflecting the expected positive change in membrane pd.