title: Hepatocellular uptake of 3H-dihydromicrocystin-LR, a cyclic peptide toxin.
abstract: The cellular uptake of microcystin-LR, a cyclic heptapeptide hepatotoxin from the cyanobacterium Microcystis aeruginosa, was studied by means of a radiolabelled derivative of the toxin. 3H-dihydromicrocystin-LR. The uptake of 3H-dihydromicrocystin-LR was shown to be specific for freshly isolated rat hepatocytes whereas the uptake in the human hepatocarcinoma cell line Hep G2 as well as the mouse fibroblast cell line NIH-3T3, and the human neuroblastoma cell line SH-SY5Y, was negligible. By means of a surface barostat technique it was shown that the membrane penetrating capacity (surface activity) of microcystin-LR was low, indicating that the toxin requires an active uptake mechanism. The hepatocellular uptake of microcystin-LR could be inhibited in the presence of bile acid transport inhibitors such as antamanide (5 microM), sulfobromophthalein (50 microM) and rifampicin (30 microM). The uptake was also reduced in a concentration dependent manner when the hepatocytes were incubated in the presence the bile salts cholate and taurocholate. A complete inhibition of the hepatocellular uptake was achieved by 100 microM of either bile salt. The overall results indicate that the uptake of microcystin-LR is through the multispecific transport system for bile acids. This mechanism of cell entry would explain the previously observed cell specificity and organotropism of microcystin-LR.
authors.affiliation: Department of Biology, Abo Akademi University, Turku, Finland.
authors.forename: J E
authors.initials: JE
authors.lastname: Eriksson
authors.forename: L
authors.initials: L
authors.lastname: Grönberg
authors.forename: S
authors.initials: S
authors.lastname: Nygård
authors.forename: J P
authors.initials: JP
authors.lastname: Slotte
authors.forename: J A
authors.initials: JA
authors.lastname: Meriluoto
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D009447:Neuroblastoma / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000378:metabolism* / Q000494:pharmacology; D012293:Rifampin / Q000494:pharmacology; D013448:Sulfobromophthalein / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D001647:Bile Acids and Salts; D010456:Peptides, Cyclic; D013448:Sulfobromophthalein; C064961:dihydromicrocystin LR; C100265:antamanide; D012293:Rifampin