- sigma Receptor ligand-induced up-regulation of the H(+)/peptide transporter PEPT1 in the human intestinal cell line Caco-2. Fujita, T., Majikawa, Y., Umehisa, S., Okada, N., Yamamoto, A., Ganapathy, V., Leibach, F.H. Biochem. Biophys. Res. Commun. (1999)