Parameters not influenced by vesamicol: Membrane potential,calcium uptake,and internal calcium concentration of synaptosomes |
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Authors: | Z Deri Vera Adam-Vizi |
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Affiliation: | (1) Department of Biochemistry II, Semmelweis University of Medicine, P. O. Box 262, H-1444 Budapest, Hungary |
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Abstract: | In our previous study vesamicol, an inhibitor of the acetylcholine transporter of the cholinergic vesicles, inhibited veratridine-evoked external Ca2+-dependent acetylcholine release from striatal slices but did not influence acetylcholine release observed in Ca2+-free medium (4). Here we examined if the effect of veratridine on membrane potential, Ca2+ uptake, and intracellular Ca2+ concentration of synaptosomes was altered by vesamicol in parallel with the inhibition of acetylcholine release. The depolarizing effect of 10 M veratridine (from 67±2.3 mV resting membrane potential to 50.7±2.5 mV) was not significantly influenced by vesamicol (1–20 M). Vesamicol (1–20 M) had no effect on either the overall curve of the veratridine-evoked45Ca2+ uptake or the amount of Ca2+ taken up by synaptosomes. Veratridine caused a rise in intrasynaptosomal Ca2+ concentration as measured by Fura2 fluorescence, and the same increase both in characteristics and in magnitude was observed in the presence of vesamicol (20 M). The K+-evoked (40 mM) increase of Ca2+ uptake and of intracellular calcium concentration were also unaltered by vesamicol. In high concentration (50 M) vesamicol inhibited both the fall in membrane potential and the elevated Ca2+ uptake by veratridine, indicating a possible nonspecific effect on potential-dependent Na+ channels at this concentration. Vesamicol, in lower concentration (20 M) when neither of the above parameters was changed, completely prevented veratridine-evoked increase of 14C]acetylcholine release. This was observed only when vesamicol was present in the media throughout the experiment after loading the preparation with 14C]choline. The results suggest that vesamicol does not interfere with veratridine-induced changes in isolated nerve terminals other than with the release of acetylcholine, thus further supporting the involvement of a vesamicol-sensitive vesicular transmitter pool in Ca2+-dependent veratridine-elicited acetylcholine release. |
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Keywords: | Vesamicol synaptosomes veratridine calcium uptake calcium concentration membrane potential |
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