Strontium, barium, and manganese metabolism in isolated presynaptic nerve terminals
To gain insight into the mechanisms by which the divalent cations Sr, Ba, and Mn affect neurotransmitter release from presynaptic nerve terminals, the authors examined the sequestration of these cations, ion comparison to Ca, by mitochondrial and nonmitochondrial organelles and the extrusion of these cations from isolated nerve terminals. Sequestration was studied in synaptosomes made leaky to small ions by treatment with saponin; efflux was examined in intact synaptosomes that were preloaded with the divalent cations by incubation in depolarizing (K rich) media. The selectivity sequence for ATP-dependent mitochondrial uptake that they observed was Mn>>Ca>Sr>>Ba, whereas that for the SER was Ca greater than or equal to Mn>Sr>>Ba. When synaptosomes that were preloaded with divalent cations were incubated in Na- and Ca-free media, there was little efflux of /sup 45/Ca, /sup 133/Ba, /sup 85/Sr, or /sup 54/Mn. When the incubation was carried out in media containing Na without Ca, there was substantial stimulation of Ca and Sr efflux, but only slight stimulation of Ba or Mn efflux. In Na-free media, the addition of 1 mM Ca promoted the efflux of all four divalent cations, probably via Ca-divalent cation exchange. In summary, the sequestration and extrusion data suggest that, with equal loads, Mn will be buffered to the greatest extent, whereas Ba will be least well buffered. These results may help to explain why Mn has a very long-lasting effect on transmitter release, while the effect of Sr is much briefer.
- Research Organization:
- Univ. of Maryland School of Medicine, Baltimore (USA)
- OSTI ID:
- 6801559
- Journal Information:
- Am. J. Physiol.; (United States), Vol. 252:6
- Country of Publication:
- United States
- Language:
- English
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BARIUM 133
METABOLISM
CATIONS
UPTAKE
MANGANESE 54
STRONTIUM 85
CALCIUM 45
CELL MEMBRANES
MITOCHONDRIA
NERVE CELLS
PHYSIOLOGY
ALKALINE EARTH ISOTOPES
ANIMAL CELLS
BARIUM ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM ISOTOPES
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CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
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HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IONS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MANGANESE ISOTOPES
MEMBRANES
NUCLEI
ODD-ODD NUCLEI
ORGANOIDS
RADIOISOTOPES
SOMATIC CELLS
STRONTIUM ISOTOPES
YEARS LIVING RADIOISOTOPES
551001* - Physiological Systems- Tracer Techniques