Mobilization of a vesamicol-insensitive pool of acetylcholine from a sympathetic ganglion by ouabain.
These experiments investigate the release of transmitter from the perfused superior cervical ganglia of cats induced by ouabain in the absence or presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol), a blocker of acetylcholine (ACh) uptake. Ouabain, perfused through the ganglia, released ACh in a Ca(2+)-dependent way. Vesamicol caused some inhibition of the release of ACh by ouabain; however, under this condition, the Na+,K(+)-ATPase inhibitor released five times more transmitter than did preganglionic stimulation at 5 Hz. Also, when ganglia exposed to vesamicol were depleted of the impulse-releasable pool of ACh, subsequent perfusion with ouabain released ACh, and this included ACh newly synthesized in the presence of vesamicol; this phenomenon could be inhibited by the lack of Ca2+ and presence of EGTA, and was completely abolished by perfusion with a medium containing 18 mM Mg2+. To test whether the release of this vesamicol-insensitive Ca(2+)-dependent pool by ouabain is associated with a decrease in the number of synaptic vesicles, ganglia treated with the ATPase inhibitor after the depletion of the impulse-releasable pool of ACh were fixed for electron microscopy. In the presence of Ca2+, coincident with the release of the vesamicol-insensitive pool of ACh, nerve terminals were almost depleted of synaptic vesicles; ganglia treated similarly, but with medium containing 18 mM Mg2+ instead of Ca2+, were not depleted of synaptic vesicles. These results suggest that ouabain releases a vesamicol-insensitive pool of ACh from the sympathetic ganglion and also support the notion that this compartment is vesicular and its exocytosis depends on extracellular Ca2+. It is suggested that empty-vesicle recycling in the presence of vesamicol restricts mobilization of full vesicles to release sites.
Department of Pharmacology and Therapeutics, McGill University, Montréal, Canada.
M A
MA
Prado
M V
MV
Gomez
B
B
Collier
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002415:Cats; D004351:Drug Resistance; D005260:Female; D005728:Ganglia, Sympathetic / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D010042:Ouabain / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology*; D013572:Synaptic Vesicles / Q000648:ultrastructure
D010880:Piperidines; C006189:vesamicol; D010042:Ouabain; D000109:Acetylcholine