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Krieger-Brauer, H. and Gratzl, Manfred (1981): Influx of Ca2+ into isolated secretory vesicles from adrenal medulla Influence of external K+ and Na+. In: FEBS Letters, Vol. 133: pp. 244-246
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Abstract

Secretory vesic1es from adrenal medulla contain catecholamines, nuc1eotides and proteins, all of which are released into the extracellular fluid during exocytosis. Adrenal medullary secretory vesic1es also contain high concentrations of Ca'+ [1]. The mechanism of the aecumulation of Ca 2+ into the vesicles is largely unknown and the experimental data eoncerning the uptake of Ca'+ into isolated secretory vesicles are contradictory. It has been reported that secretory vesicle membranes are impermeable to Ca'+ [2], that secretory vesicles take up Ca 2+ independently of ATP [3] and that they possess an ATP-stimulated uptake system [4,5]. In earlier work relatively impure and unstable seeretory vesicle fractions were used for the determination of Ca 2+ -uptake. We have developed a method to isolate highly purified and stable secretory vesicles from bovine medulla [6]. With these vesic1es we repeated earlier Ca'+ -uptake experiments and found that: (i) The vesic1es take up <sCa2+ in K+-containingmedia; (ü) 4SCa2+ uptake is abolished in the presence ofNa+; (üi) nie Ca 2+ content of isolated secretory vesic1es is increased when incubated with Ca 2+ in media containing K+, but not in media containing Na +.