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Sequestration of depolarization-induced Ca2+ loads by mitochondria and Ca2+ efflux via mitochondrial Na+/Ca2+ exchanger in bovine adrenal chromaffin cells



Sequestration of depolarization-induced Ca2+ loads by mitochondria and Ca2+ efflux via mitochondrial Na+/Ca2+ exchanger in bovine adrenal chromaffin cells



Japanese Journal of Physiology 49(1): 35-46



We used fura-2 microfluorometry to investigate the role of mitochondria in regulating the increase in the cytosolic Ca2+ concentration ((Ca)in) and the mechanism(s) underlying the subsequent Ca2+ efflux from mitochondria in bovine adrenal chromaffin cells. The rate of (Ca)in decay during and following stimulation with 100 mM KCl depolarization was markedly increased when the mitochondrial Na+/Ca2+ exchanger was inhibited by clonazepam or CGP-37157(CGP). In contrast, the addition of gramicidin, which increased the cytosolic Na+ concentration, following KCl depolarization caused a secondary increase in (Ca)in. This secondary increase in (Ca)in was prevented by the addition of clonazepam or CGP, and by the removal of external Na+. The subsequent removal of clonazepam or CGP, or the delayed addition of Na+ caused a slow increase in (Ca)in. A protonophore (FCCP) applied following KCl depolarization also caused a robust, secondary increase in (Ca)in, which was insensitive to blocking by clonazepam or CGP. Neither gramicidin nor FCCP altered the (Ca)in decay when applied following stimulation with histamine or caffeine, which mobilized Ca2+ from intracellular stores. These results suggest that the large (Ca)in increase induced by Ca2+ influx, but not by intracellular Ca2+ release, is buffered by mitochondria, and that the mitochondrial Na+/Ca2+ exchanger makes a major contribution to the subsequent Ca2+ efflux from mitochondria.

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Accession: 011345159

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PMID: 10219107


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