title: ATP-stimulated Ca2+ transport into cholinergic Torpedo synaptic vesicles.
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 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.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004557:Electric Organ / Q000378:metabolism*; D005399:Fishes; D007700:Kinetics; D008634:Mersalyl / Q000494:pharmacology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000001:Calcimycin; D008634:Mersalyl; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium