Distinct transport characteristics of basolateral peptide transporters between MDCK and Caco-2 cells.

The cellular polarity of [14C]glycylsarcosine (Gly-Sar) transport in Madin-Darby canine kidney (MDCK) cells was compared with that in the human intestinal cell line Caco-2. In MDCK cells, [14C]Gly-Sar accumulation was greater at the basolateral side than at the apical side, and there was little net transcellular transport. In Caco-2 cells, [14C]Gly-Sar accumulation was greater at the apical side and unidirectional transcellular transport occurred from the apical to basolateral side. Efflux of [14C]Gly-Sar from MDCK cells to either side was negligible, whereas that from Caco-2 cells was significantly faster to the basolateral side. The basolateral peptide transporter in MDCK cells possessed a similar substrate specificity, but a much higher substrate affinity, than that in Caco-2 cells. The basolateral peptide transporter in MDCK cells did not accumulate Gly-Sar during hypertonic stress. These findings indicate that the basolateral peptide transporter in MDCK cells is involved in the cellular uptake of small peptides, but not in the extrusion of small peptides to the extracellular space.