ATP-dependent calcium uptake by cholinergic synaptic vesicles isolated from Torpedo electric organ

Cholinergic synaptic vesicles were purified from Torpedo electric organ to near morphological homogeneity. They were isolated in a K+ environment. A method is described for the preparation of concentrated synaptic vesicles that allows uptake studies by conventional techniques. An ATP-Mg-dependent calcium uptake associated with synaptic vesicles is characterized. The uptake system transports calcium against a high concentration gradient. The maximum accumulation rate is obtained for the calcium, Mg++ and ATP concentrations likely to be found in the nerve terminal cytoplasm. It is suggested that synaptic vesicles are implicated in the removal of the calcium entering the nerve terminal during synaptic activity.