Intracellular sodium modulates mitochondrial calcium signaling in vascular endothelial cells.
We have investigated the role of extramitochondrial Na(+) for the regulation of mitochondrial Ca(2+) concentration ([Ca(2+)](m)) in permeabilized single vascular endothelial cells. [Ca(2+)](m) was measured by loading the cells with the membrane-permeant Ca(2+) indicator fluo-3/AM and subsequent removal of cytoplasmic fluo-3 by surface membrane permeabilization with digitonin. An elevation of extramitochondrial Ca(2+) resulted in a dose-dependent increase in the rate of Ca(2+) accumulation into mitochondria (k(0.5) = 3 microm) via the mitochondrial Ca(2+) uniporter. In the presence of 10 mm extramitochondrial Na(+) ([Na(+)](em)), repetitive application of brief pulses of high Ca(2+) (2-10 microm) to simulate cytoplasmic [Ca(2+)] oscillations caused transient increases of [Ca(2+)](m) characterized by a fast rising phase that was followed by a slow decay. Removal of extramitochondrial Na(+) or inhibition of mitochondrial Na(+)/Ca(2+) exchange with clonazepam blocked mitochondrial Ca(2+) efflux and resulted in a net accumulation of Ca(2+) by the mitochondria. Half-maximal activation of mitochondrial Na(+)/Ca(2+) exchange occurred at [Na(+)](em) = 4.4 mm, which is well within the physiological range of cytoplasmic [Na(+)]. This study provides evidence that Ca(2+) efflux from the mitochondria in vascular endothelial cells occurs solely via Na(+)/Ca(2+) exchange and emphasizes the important role of intracellular Na(+) for mitochondrial Ca(2+) regulation.
Sedova
M
M
Loyola University Chicago, Stritch School of Medicine, Department of Physiology, Maywood, Illinois 60153, USA.
Blatter
L A
LA
D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics*; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002998:Clonazepam / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000494:pharmacology; D007202:Indicators and Reagents / Q000494:pharmacology; D007700:Kinetics; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D015398:Signal Transduction; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D013050:Spectrometry, Fluorescence; D014966:Xanthenes / Q000494:pharmacology
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D014966:Xanthenes; C059715:Fluo-3; D002998:Clonazepam; D012964:Sodium; D004072:Digitonin; D002118:Calcium