Proton gradient linkage to active uptake of [3H]acetylcholine by Torpedo electric organ synaptic vesicles

Abstract

It has been confirmed that cholinergic synaptic vesicles isolated from the electric organ of Torpedo californica exhibit adenosine 5'-triphosphate (ATP) dependent active uptake of [3H]acetylcholine. Active uptake can be completely inhibited by low concentrations of the mitochondrial uncouplers carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone, nigericin, gramicidin, valinomycin, and A 23187. Under similar conditions uncouplers stimulate the vesicle adenosinetriphosphatase (ATPase) by from 40 to 80%. ATP-supported uptake of [3H]acetylcholine increases greatly as the external pH is increased from 6.6 to 7.6 and remains approximately constant from pH 7.8 to pH 8.6. The uptake also becomes more selective for [3H]acetylcholine compared to [14C]choline as the pH is increased from 6.6 to 7.6, achieving 12-fold selectively, in a manner similar to the increase in the amount of [3H]acetylcholine taken up. Bicarbonate stimulates both the amount and selectivity of [3H]acetylcholine uptake over the lower pH range, but it has no effect over the higher pH range. Exogenous ammonium ion completely inhibits active [3H]acetylcholine uptake, with lower concentrations of ammonium ion required at higher pH values in a manner consistent with ammonia being the active species. Adenosine 5'-diphosphate and a nonhydrolyzable ATP analogue do not support active [3H]acetylcholine uptake. It is concluded that an ATPase pumps protons into the cholinergic synaptic vesicle to produce an internally acidic and positively charged proton gradient that is linked to [3H]acetylcholine uptake.