Sequestration of depolarization-induced Ca2+ loads by mitochondria and Ca2+ efflux via mitochondrial Na+/Ca2+ exchanger in bovine adrenal chromaffin cells.
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.
Sorimachi
M
M
Department of Physiology, Kagoshima University School of Medicine, Kagoshima, 890-8520, Japan. ciliary@med2.kufm.kagoshima-u.ac.jp
Nishimura
S
S
Yamagami
K
K
D000311:Adrenal Glands / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002417:Cattle; D019439:Chromaffin Cells / Q000502:physiology* / Q000648:ultrastructure*; D002998:Clonazepam / Q000031:analogs & derivatives / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology; D008564:Membrane Potentials; D008928:Mitochondria / Q000502:physiology*; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D013841:Thiazepines / Q000494:pharmacology
D018757:GABA Modulators; D019831:Sodium-Calcium Exchanger; D013841:Thiazepines; D002998:Clonazepam; C079032:CGP 37157; D002118:Calcium