Co-operative action of calcium ions in dopamine release from rat brain synaptosomes.
1. The release of [3H]dopamine from isolated presynaptic nerve terminals (synaptosomes) prepared from rat striata was measured as a function of the external Ca2+ concentration ([Ca2+]o). 2. In synaptosomes depolarized by the addition of 50 mM-K+, release of [3H]dopamine increased in a highly non-linear manner with [Ca2+]o. The release could be described as a third power function of [Ca2+]o. 3. Both 45Ca2+ influx and the change in the free cytosolic Ca2+ concentration ([Ca2+]i, measured with the fluorescent Ca2+ indicator fura-2) that were evoked by depolarization increased in a linear manner with [Ca2+]o. 4. These results suggest that non-linearity in the [Ca2+]o dependence of transmitter release originates in a co-operative relation between [Ca2+]i and exocytosis.
Nachshen
D A
DA
Department of Physiology, Cornell University Medical College, New York, NY 10021.
Sanchez-Armass
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S
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D066298:In Vitro Techniques; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism*
D011188:Potassium; D002118:Calcium; D004298:Dopamine