ATP-stimulated Ca2+ transport into cholinergic Torpedo synaptic vesicles.


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 microM, and Vmax = 3 +/- 0.3 nmol Ca2+/mg protein/min. Treatment of the vesicles with mersalyl, dicyclohexylcarbodiimide, 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.


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@article{Michaelson1980ATPstimulatedCT, title={ATP-stimulated Ca2+ transport into cholinergic Torpedo synaptic vesicles.}, author={Daniel M. Michaelson and Ilana Ophir and Irene Angel}, journal={Journal of neurochemistry}, year={1980}, volume={35 1}, pages={116-24} }