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Is the Augmentation of K + ‐Evoked Intrasynaptosomal Ca 2+ Concentration Due to the Influx of Ca 2+ in Rat Brain Synaptosomes?
Author(s) -
Okada Mitsuko,
Mine Kazunori,
Iwasaki Katsunori,
Fujiwara Michihiro
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb07265.x
Subject(s) - verapamil , extracellular , cytosol , channel blocker , chemistry , nifedipine , egta , depolarization , diltiazem , synaptosome , biophysics , calcium , endocrinology , medicine , acidosis , biochemistry , biology , enzyme , organic chemistry
Intraterminal free Ca 2+ concentration modulates the subsequent release of neurotransmitters. Depolarization of synaptosomes with 29 m M K + augments cytosolic free Ca 2+ concentration, which is triphasic, the peak times being at 10, 60, and 180 s. We examined the characteristics of each elevation of cytosolic free Ca 2+ concentration in rat brain synaptosomes which had been preincubated for 3 min with a Ca 2+ ‐channel blocker, such as La 3+ , diltiazem, nifedipine, or verapamil, and under conditions of hypoxia or acidosis. The concentration of free Ca 2+ in the quin‐2‐loaded rat brain synaptosomes was detected fluorometrically. All these elevations were suppressed in the presence of 200 μ M EGTA or 100 μ M La 3+ . At the first phase, the elevation of cytosolic free Ca 2+ concentration with high K + stimuli was significantly inhibited by La 3+ (20 μ M ) or by acidosis (pH 6.7). On the other hand, diltiazem, which is a more potent blocker of the release of Ca 2+ from the mitochondria, inhibited the increasing cytosolic free Ca 2+ concentration at the third phase in a concentration‐dependent manner. Hypoxia also showed inhibition at the third phase. These results suggest that the augmentation of high K + ‐evoked cytosolic free Ca 2+ concentration may be due to the influx of extracellular Ca 2+ . The increase in cytosolic free Ca 2+ concentration at the third phase is no doubt linked to the mitochondrial function.