Neurochemical Research

, Volume 14, Issue 7, pp 677–682 | Cite as

Lack of excitatory amino acid-induced effects on calcium fluxes measured with45Ca2+ in rat cerebral cortex synaptosomes

  • Michele Simonato
  • Richard S. Jope
  • Clementina Bianchi
  • Lorenzo Beani
Original Articles

Abstract

Ca2+ uptake was measured in purified rat cerebral cortex synaptosomes (P3 pellets) using45Ca2+ as a tracer. Ca2+ influx increased in time, and with an increase in external K+ concentration and temperature. The net (external K+-induced, depolarization-dependent) uptake follows a two-component course. The exponential term, due to the opening of voltage-operated calcium channels (VOC), has a rate constant which increases with an increase in the depolarization level (1.04 versus 0.54 nmol/s/mg protein for 50 mM—versus 15 mM [K+]-dependent net influx). The linear term, due to the Na+/Ca2+ exchange system, has a similar rate constant at all depolarization levels (0.16+/−0.05 and 0.11+/−0.02 nmol/s/mg protein). Excitatory amino acids (glutamate, kainate and n-methyl-d-aspartate-NMDA-) were tested on this preparation at doses ranging between 5×10−5 M and 5×10−3M and at multiple incubation times, under resting conditions and under two depolarizing conditions (partial depolarization: 15 mM external K+ and maximal depolarization: 50 mM external K+). NMDA was also tested in the absence of Mg2+. No effect was detectable under any of these experimental conditions. Hypotheses to interpret these data are discussed. Further studies on other preparations are needed in order to directly investigate the presynaptic effects of excitatory amino acids.

Key words

Synaptosomes calcium fluxes glutamate kainate NMDA 

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Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • Michele Simonato
    • 1
  • Richard S. Jope
    • 2
  • Clementina Bianchi
    • 1
  • Lorenzo Beani
    • 1
  1. 1.Institute of PharmacologyUniversity of FerraraFerraraItaly
  2. 2.Department of Pharmacology and Neuropsychiatry Research ProgramUniversity of Alabama at BirminghamBirminghamUSA

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