Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract In neuroblastoma cells, the intracellular thiamine triphosphate (TTP) concentration was found to be about 0.5 μ m, which is several times above the amount of cultured neurons or glial cells. In inside-out patches, addition of TTP (1 or 10) μ m 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 (P o) shows a bell-shaped behavior as a function of pipette potential (V p). P o is maximal for −25 mV〈V p〈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 V p=−20 mV but had the opposite effect at +30 mV. This finding corresponds to a shift of P o 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.
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