Abstract: Activation of the Ca2+/Mg2+ ATPase associated with highly purified Torpedo synaptic vesicles results in 45Ca2+ uptake. The accumulated 45Ca2+ is released by hypoosmotic buffer and by the Ca2+ ionophore A23187. Density‐gradient centrifugation and permeation chromatography reveal that vesicular acetylcholine and the membrane‐bound 45Ca2+ co‐migrate, thus implying that 45Ca2+ is transported into cholinergic vesicles. ATP‐dependent 45Ca2+ uptake follows saturation kinetics, with KmCa2+= 50 μM, KmATP= 5 μM, and Vmax= 3 ± 0.3 nmol Ca2+/mg protein/min. Treatment of the vesicles with mersalyl, dicyclohexyl‐carbodiimide, and quercetin leads to inactivation of the Ca2+/Mg2+ ATPase and to comparable inhibition of 45Ca2+ transport. Ruthenium red and ouabain have no effect on either of these activities. Nigericin in the presence of external K+ is a potent inhibitor of 45Ca2+ translocation, whereas gramicidin activates transport. The proton translocator carbonylcyanide p‐trifluoromethoxy‐phenylhydrazone (FCCP) and FCCP + the ionophore valinomycin partially inhibit 45Ca2+ transport. By contrast, the above ionophores do not affect Ca2+/Mg2+ ATPase activity. Tentative mechanisms for ATP‐dependent Ca2+ transport into cholinergic synaptic vesicles and the physiological significance of this process are discussed.
|Number of pages||9|
|Journal||Journal of Neurochemistry|
|State||Published - Jul 1980|