Ca2(+)-surrogate action of Pb2+ on acetylcholine release from rat brain synaptosomes.
The effect of lead ions on the release of acetylcholine (ACh) was investigated in intact and digitonin-permeabilized rat cerebrocortical synaptosomes that had been prelabeled with [3H]choline. Release of ACh was inferred from the release of total 3H label or by determination of [3H]ACh. Application of 1 microM Pb2+ to intact synaptosomes in Ca2(+)-deficient medium induced 3H release, which was enhanced by K+ depolarization. This suggests that entry of Pb2+ into synaptosomes and Pb2(+)-induced ACh release can be augmented by activation of the voltage-gated Ca2+ channels in nerve terminals. The lead-induced release of [3H]ACh was blocked by treatment of synaptosomes with vesamicol, which prevents uptake of ACh into synaptic vesicles without affecting its synthesis in the synaptoplasm. This indicates that Pb2+ selectively activates the release of a vesicular fraction of the transmitter with little or no effect on the leakage of cytoplasmic ACh. Application of 1-50 nM (EC50 congruent to 4 nM) free Pb2+ to digitonin-permeabilized synaptosomes elicited release of 3H label that was comparable with the release induced by 0.2-5 microM (EC50 congruent to 0.5 microM) free Ca2+. This suggests that Pb2+ triggers transmitter exocytosis directly and that it is a some 100 times more effective activator of exocytosis than is the natural agonist Ca2+.
Shao
Z
Z
Department of Physiology and Biophysics, University of Cincinnati School of Medicine, Ohio.
Suszkiw
J B
JB
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002463:Cell Membrane Permeability; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D004072:Digitonin; D005089:Exocytosis / Q000187:drug effects; D007854:Lead / Q000494:pharmacology*; D008297:Male; D010880:Piperidines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D010880:Piperidines; D007854:Lead; C006189:vesamicol; D004072:Digitonin; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium