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23 April 2003

Characteristics of the hypoosmosis-induced calcium response in isolated nerve terminals of rat brain.

Alexander V. Levko, Anatoly A. Rakovich, Svetlana G. Samoilenko, Sergei V. Konev

Med Sci Monit 2003; 9(4): BR115-124 :: ID: 4706

Abstract

BACKGROUND: Cerebral edema contributes significantly to morbidity and death in many common neurological disorders. Ca[sup]2+[/sup] ions play a important role in the development of pathophysiological reactions in nerve cells. The aim of our research was to elucidate the mechanism of the osmotically-induced entrance of Ca[sup]2+[/sup] into nerve terminals (synaptosomes) and to estimate the involvement of endoplasmic reticulum Ca[sup]2+[/sup] stores in intrasynaptosomal Ca[sup]2+[/sup]-dependent processes in hypoosmotic swelling. MATERIAL/METHODS: Synaptosomes were isolated from rat brains. The rates of Ca[sup]2+[/sup]uptake were determined using [sup]45[/sup]Ca[sup]2+[/sup] as a radiotracer. Intracellular Ca[sup]2+[/sup] measurements were performed using Fura-2 as a cell calcium indicator. RESULTS: Entry into synaptosomes in hypotonic medium (230 mOsm) of osmosis-induced Ca[sup]2+[/sup] ([sup]45[/sup] Ca[sup]2+[/sup]) was reduced by verapamil, Cd[sup]2+[/sup] or genistein to 50-60% of baseline. NEM and PCMB inhibit [sup]45[/sup]Ca[sup]2+[/sup] uptake. Swelling of synaptosomes is coupled with increased tyrosine kinase activity and oxidation of SH-groups of cysteine residues of the membrane proteins involved in Ca[sup]2+[/sup] transport. These membrane processes probably influence the properties of voltage-dependent L-type Ca[sup]2+[/sup] channels, which increase their conductivity to Ca[sup]2+[/sup]. Activation of RyR- and Ins(1,4,5,)P[sub]3[/sub]-stores were recorded. It was shown that the Ins(1,4,5,)P[sub]3[/sub]-stores are a major source of the increase in [Ca[sup]2+[/sup]]i in the cytoplasm with swelling of the synaptosomes. CONCLUSIONS: Osmotic swelling of synaptosomes leads to Ca[sup]2+[/sup] accumulation by intrasynaptosomal mitochondria. Excess Ca[sup]2+[/sup] ions stored in mitochondria inhibit oxidative phosphorylation. This causes an irreversible reduction in the energy status of nerve terminals, which can initiate pathophysiological processes in nerve cells.

Keywords: Fura-2 - diagnostic use, Osmotic Pressure - drug effects, Protein-Tyrosine Kinases - analysis

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Medical Science Monitor eISSN: 1643-3750
Medical Science Monitor eISSN: 1643-3750