Parameters not influenced by vesamicol: membrane potential, calcium uptake, and internal calcium concentration of synaptosomes.
In our previous study vesamicol, an inhibitor of the acetylcholine transporter of the cholinergic vesicles, inhibited veratridine-evoked external Ca(2+)-dependent acetylcholine release from striatal slices but did not influence acetylcholine release observed in Ca(2+)-free medium (4). Here we examined if the effect of veratridine on membrane potential, Ca(2+)-uptake, and intracellular Ca2+ concentration of synaptosomes was altered by vesamicol in parallel with the inhibition of acetylcholine release. The depolarizing effect of 10 microM veratridine (from 67 +/- 2.3 mV resting membrane potential to 50.7 +/- 2.5 mV) was not significantly influenced by vesamicol (1-20 microM). Vesamicol (1-20 microM) had no effect on either the overall curve of the veratridine-evoked 45Ca2+ 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 microM). The K(+)-evoked (40 mM) increase of Ca2+ uptake and of intracellular calcium concentration were also unaltered by vesamicol. In high concentration (50 microM) 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 microM) 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Deri
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Department of Biochemistry II, Semmelweis University of Medicine, Budapest, Hungary.
Adam-Vizi
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V
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016257:Fura-2; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D014701:Veratridine / Q000494:pharmacology*
D009467:Neuromuscular Depolarizing Agents; D010880:Piperidines; C006189:vesamicol; D014701:Veratridine; D012964:Sodium; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D016257:Fura-2