Thiamin and derivatives as modulators of rat brain chloride channels.
Several membrane fractions were prepared from rat brain by differential and sucrose density gradient centrifugation. Most fractions took up 36Cl- rapidly at a rate linear with time during the first 30-60 s, then the rate progressively slowed down. The lowest rate of uptake was found in the mitochondrial fraction. Oxythiamin partially inhibited 36Cl- uptake in all fractions. In P2 (crude synaptosomal fraction), oxythiamin decreased the initial rate of uptake by 32%, the apparent Ki being 1.5 mM. Thiamin and amprolium were less effective as inhibitors. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (0.1-1 mM) inhibited 36Cl- uptake by 40-50%. In the presence of this compound at a concentration > or = 5 x 10(-4) M, oxythiamin became ineffective. 36Cl- uptake was increased by GABA (0.1 mM) and this effect was antagonized by picrotoxin as expected, but not by oxythiamin. The rate of 36Cl- uptake did not appreciably depend on the external chloride concentration and was unaffected by bumetanide or by replacement of external Na+ by choline. Taken together, these data suggest that the oxythiamin-sensitive 36Cl- influx is essentially diffusional and is not related to the GABA receptor or the Na:K:2Cl co-transport. Partial replacement of external Na+ by K+ or treatment with 0.1 mM veratridine (which should both result in membrane depolarization) increased 36Cl- uptake by 50 and 30% respectively; the inhibitory effect of oxythiamin was enhanced to the same proportion.(ABSTRACT TRUNCATED AT 250 WORDS)
Bettendorff
L
L
Laboratory of General and Comparative Biochemistry, University of Liège, Belgium.
Hennuy
B
B
Wins
P
P
Schoffeniels
E
E
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000241:Adenosine / Q000494:pharmacology; D000670:Amprolium / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D005260:Female; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins / Q000187:drug effects / Q000502:physiology*; D009928:Organ Specificity; D010119:Oxythiamine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000378:metabolism; D013831:Thiamine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014701:Veratridine / Q000494:pharmacology
D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D010119:Oxythiamine; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D011189:Potassium Chloride; D014701:Veratridine; D000670:Amprolium; D000241:Adenosine; D002794:Choline; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D013831:Thiamine