Acetylcholine release from isolated synaptic vesicles related to ionic permeability changes: continuous detection with a chemiluminescent method.
The effect of ionic permeability changes on acetylcholine (ACh) release from isolated cholinergic synaptic vesicles of Torpedo was studied using a chemiluminescent method for continuous ACh detection. Vesicles rendered freely permeable to potassium by valinomycin lost most of their ACh content in K+ media, if the accompanying anion was permeant; it thus appeared that ACh leakage occurred as the result of internal osmotic changes. Upon addition of ionophores that catalyse monovalent cation/H+ exchange (gramicidin D or a mixture of valinomycin plus protonophore FCCP), a rapid but transient ACh release was observed. Surprisingly, nigericin which also catalyses K+/H+ exchange, had no effect on ACh release. The divalent cation ionophore A23187 promoted ACh release only when calcium (and not magnesium) was introduced into the external medium in a millimolar concentration range. As the simultaneous addition of the protonophore FCCP and A23187 decreased this calcium-dependent ACh leakage, a releasing effect of A23187 through Ca2+/H+ exchange is suspected. The present results emphasise the role of internal protons for ACh retention inside synaptic vesicles.
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002412:Cations; D002463:Cell Membrane Permeability / Q000187:drug effects; D004557:Electric Organ / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D008163:Luminescent Measurements; D011188:Potassium / Q000378:metabolism; D011522:Protons; D012964:Sodium / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism*; D014101:Torpedo / Q000378:metabolism*
D002412:Cations; D007476:Ionophores; D011522:Protons; D012964:Sodium; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium