Adenosine Triphosphate-Dependent Calcium Uptake of Synaptic Vesicle Fraction is Largely Due to Contaminating Microsomes

Abstract

Ca²⁺ uptake by synaptic vesicle fractions isolated from bovine caudatolenticular nuclei and from rat brain was studied. The purified vesicle fractions from both materials took up very little Ca²⁺ even in the presence of ATP and Mg²⁺, but the crude fractions took up Ca²⁺ actively, showing the maximum uptake around pH 7.0. Since the crude fractions were contaminated by microsomes, which are known to accumulate Ca²⁺ actively (Yoshida, H., Kadota, K., & Fujisawa, H. (1966) Nature 212, 291-292; Otsuka, M., Ohtsuki, I., & Ebashi, S. (1965) J. Biochem. 58, 188-190), the active uptake of Ca²⁺ appeared to be largely, if not wholly, due to microsomal contamination.