title: Thiamine triphosphate activates an anion channel of large unit conductance in neuroblastoma cells.
abstract: In neuroblastoma cells, the intracellular thiamine triphosphate (TTP) concentration was found to be about 0.5 microM, which is several times above the amount of cultured neurons or glial cells. In inside-out patches, addition of TTP (1 or 10 microM) to the bath activated an anion channel of large unit conductance (350-400 pS) in symmetrical 150 mM NaCl solution. The activation occurred after a delay of about 4 min and was not reversed when TTP was washed out. A possible explanation is that the channel has been irreversibly phosphorylated by TTP. The channel open probability (Po) shows a bell-shaped behavior as a function of pipette potential (Vp). Po is maximal for -25 mV < Vp < 10 mV and steeply decreases outside this potential range. From reversal potentials, permeability ratios of PCl/PNa = 20 and PCl/Pgluconate = 3 were estimated. ATP (5 mM) at the cytoplasmic side of the channel decreased the mean single channel conductance by about 50%, but thiamine derivatives did not affect unit conductance; 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.1 mM) increased the flickering of the channel between the open and closed state, finally leading to its closure. Addition of oxythiamine (1 mM), a thiamine antimetabolite, to the pipette filling solution potentiates the time-dependent inactivation of the channel at Vp = -20 mV but had the opposite effect at +30 mV. This finding corresponds to a shift of Po towards more negative resting membrane potentials. These observations agree with our previous results showing a modulation of chloride permeability by thiamine derivatives in membrane vesicles from rat brain.
authors.affiliation: Laboratory of General and Comparative Biochemistry, University of Liège, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Bettendorff
authors.forename: H A
authors.initials: HA
authors.lastname: Kolb
authors.forename: E
authors.initials: E
authors.lastname: Schoffeniels
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D018118:Chloride Channels / Q000187:drug effects* / Q000378:metabolism; D004553:Electric Conductivity; D008564:Membrane Potentials; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism*; D010119:Oxythiamine / Q000494:pharmacology; D010766:Phosphorylation; D013838:Thiamine Triphosphate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D018118:Chloride Channels; D010119:Oxythiamine; D013838:Thiamine Triphosphate; D000255:Adenosine Triphosphate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid