96 research outputs found
Influx of Ca2+ into isolated secretory vesicles from adrenal medulla Influence of external K+ and Na+
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 +
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