Nerve endings are characterized morphologicallyby the presence of a large number of small vesicles. These synaptic vesicles are generally accepted as the site of neurotr~~itter storage [ 1,2] , Recently, evidence from several laboratories indicated [3,4] that beside their function in storing and releasing neurotransmitters, synaptic vesicles exhibit an ATPdependent calcium uptake. To date, direct evidence does not exist that these two functions, neurotr~s-mitter storage and calcium transport, reside in the same or two separate populations of vesicles. For this reason we refer to the organelle that transports calcium as synaptosomal vesicle [4] .Synaptic vesicles from Torpedct ma~~rata [S] and coated synaptic vesicles from calf brain 13 ] were shown to possess Ca-Mg ATPase. ATPase from synaptic vesicles of guinea pig brain was activated [6] by magnesium and partially by calcium. We report here that rat brain synaptosom~ vesicles possess a Mg-ATPase activity which is associated with the calcium transport of rat brain synaptosomal vesicles.
MethodsSynaptosomal vesicles were prepared by centrifuging rat brain synaptosom~ lysates at 100 000 X g for 60 min as in [4]. Calcium transport studies were performed with '%aCla (The Radiochemical Centre, Amer.&am) using the millipore fdtration technique. Following incubation at 22°C the reactions were stopped by quick dilution with ice cold 0.1 S M NaCl ~Ssevi~~~orth-Roland Biomedical Press and rapidly faltered through 0.45 pm millipore filters.
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