title: Membrane depolarization in LA-N-1 cells. The effect of maitotoxin is Ca(2+)- and Na(+)-dependent.
abstract: We investigated the influence of ion compositions on the membrane potential in LA-N-1 human neuroblastoma cells using bisoxonol as a potential-sensitive fluorescent dye. The ability of K+, ouabain, veratridine, and maitotoxin to induce membrane depolarization was evaluated. Increasing concentrations of K+ ions from 10 to 50 mM caused a dose-dependent increase of bisoxonol fluorescence, which was completely independent on Na+ and Ca2+. Ouabain (5 mM), an inhibitor of the Na+, K(+)-ATPase, failed to induce membrane depolarization. Veratridine (40 and 100 microM), a Na+ channel activator, only in the presence of 10 micrograms of Leiurus scorpion venom reduced the membrane potential. Maitotoxin (MTX) from 3 to 10 ng/mL depolarized LA-N-1 cells in a dose-dependent manner, and produced a rapid and sustained increase of intracellular free calcium monitored by means of fluorescent probe fura-2. The MTX-induced depolarization and the increase in cytosolic free calcium concentration were dependent on extracellular Ca2+ ions. On the other hand, Na+ ions also seem to be, although only partially, implicated in the MTX effects, since both the blockade of tetrodotoxin (TTX)-sensitive voltage-operated Na+ channels and the removal of Na+ ions were able to reduce the depolarization. In conclusion, our data indicate that the depolarizing action of MTX on LA-N-1 cells is Ca(2+)- and Na(+)-dependent, although the latter only partially, and that this effect is dependent on Ca2+ influx into the cells likely through a voltage-insensitive calcium-entry system.
authors.affiliation: Institute of Neurological Sciences, Faculty of Medicine, 2nd University of Naples, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Sorrentino
authors.forename: M R
authors.initials: MR
authors.lastname: Monsurrõ
authors.forename: I N
authors.initials: IN
authors.lastname: Singh
authors.forename: J N
authors.initials: JN
authors.lastname: Kanfer
mesh_terms: D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D003600:Cytosol / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008387:Marine Toxins / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D010042:Ouabain / Q000494:pharmacology; D035964:Oxocins; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014701:Veratridine / Q000494:pharmacology; D000095702:Polyether Toxins
chemical_list: D002118:Calcium; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010042:Ouabain; D035964:Oxocins; D011188:Potassium; D012964:Sodium; D014701:Veratridine; C020394:maitotoxin; D000095702:Polyether Toxins