Maitotoxin-induced calcium influx in erythrocyte ghosts and rat glioma C6 cells, and blockade by gangliosides and other membrane lipids.
Maitotoxin (MTX) at 0.3 nM elicited a 10-20-fold increase in the level of Ca(2+) influx in rat glioma C6 cells. At higher doses (3-30 nM), MTX induced marked Ca(2+) influx in human erythrocyte ghosts when monitored with the fluorescent dye Fura-2. Although the ghosts were not as susceptible to MTX as intact erythrocytes or other cell lines, Fura-2 experiments under various conditions suggested that the MTX-induced entry of ions into the ghosts was mediated by a mechanism similar to that reported for cells or tissues. These ghosts are the simplest system known to be sensitive to MTX and thus may be suitable for research on the direct action of MTX. Gangliosides GM1 and GM3, glycosphingolipids which have a sialic acid residue, strongly inhibited MTX-induced Ca(2+) influx in C6 cells, while the inhibitory action by asialo-GM1, which lacks a sialic acid residue, was somewhat weaker. Their inhibitory potencies were in the following order: GM1 (IC(50) approximately 2 microM) > GM3 (IC(50) approximately 5 microM) > asialo-GM1 (IC(50) approximately 20 microM). GM1 (3 microM) completely blocked MTX (30 nM)-induced Ca(2+) influx in human erythrocyte ghosts. When C6 cells were pretreated with tunicamycin, an antibiotic which inhibits N-linked glycosylation, or concanavalin A, a lectin which exhibits a high affinity for cell-surface oligosaccharides, MTX-induced Ca(2+) influx was significantly potentiated. This suggests that removal of oligosaccharides from the cell surface by tunicamycin or capping of sugar chains on plasma membranes by concanavalin A can potentiate the action of MTX.
Konoki
K
K
Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Hashimoto
M
M
Murata
M
M
Tachibana
K
K
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001932:Brain Neoplasms / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D002132:Calcium Radioisotopes; D003208:Concanavalin A / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D005732:Gangliosides / Q000494:pharmacology; D005910:Glioma / Q000378:metabolism*; D008387:Marine Toxins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008563:Membrane Lipids / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008958:Models, Molecular; D008968:Molecular Conformation; D035964:Oxocins; D051381:Rats; D014407:Tumor Cells, Cultured; D014415:Tunicamycin / Q000494:pharmacology; D000095702:Polyether Toxins
D000900:Anti-Bacterial Agents; D002118:Calcium; D002132:Calcium Radioisotopes; D003208:Concanavalin A; D005456:Fluorescent Dyes; D016257:Fura-2; D005732:Gangliosides; D008387:Marine Toxins; D008563:Membrane Lipids; D035964:Oxocins; D014415:Tunicamycin; C020394:maitotoxin; D000095702:Polyether Toxins