Sustained Ca2+ transfer across mitochondria is Essential for mitochondrial Ca2+ buffering, sore-operated Ca2+ entry, and Ca2+ store refilling.
Mitochondria have been found to sequester and release Ca2+ during cell stimulation with inositol 1,4,5-triphosphate-generating agonists, thereby generating subplasmalemmal microdomains of low Ca2+ that sustain activity of capacitative Ca2+ entry (CCE). Procedures that prevent mitochondrial Ca2+ uptake inhibit local Ca2+ buffering and CCE, but it is not clear whether Ca2+ has to transit through or remains trapped in the mitochondria. Thus, we analyzed the contribution of mitochondrial Ca2+ efflux on the ability of mitochondria to buffer subplasmalemmal Ca2+, to maintain CCE, and to facilitate endoplasmic reticulum (ER) refilling in endothelial cells. Upon the addition of histamine, the initial mitochondrial Ca2+ transient, monitored with ratio-metric-pericam-mitochondria, was largely independent of extracellular Ca2+. However, subsequent removal of extracellular Ca2+ produced a reversible decrease in [Ca2+]mito, indicating that Ca2+ was continuously taken up and released by mitochondria, although [Ca2+]mito had returned to basal levels. Accordingly, inhibition of the mitochondrial Na+/Ca2+ exchanger with CGP 37157 increased [Ca2+]mito and abolished the ability of mitochondria to buffer subplasmalemmal Ca2+, resulting in an increased activity of BKCa channels and a decrease in CCE. Hence, CGP 37157 also reversibly inhibited ER refilling during cell stimulation. These effects of CGP 37157 were mimicked if mitochondrial Ca2+ uptake was prevented with oligomycin/antimycin A. Thus, during cell stimulation a continuous Ca2+ flux through mitochondria underlies the ability of mitochondria to generate subplasmalemmal microdomains of low Ca2+, to facilitate CCE, and to relay Ca2+ from the plasma membrane to the ER.
Malli
Roland
R
Department of Medical Biochemistry and Medical Molecular Biology, University of Graz, 8010 Graz, Austria.
Frieden
Maud
M
Osibow
Karin
K
Zoratti
Cristina
C
Mayer
Mirza
M
Demaurex
Nicolas
N
Graier
Wolfgang F
WF
D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D002998:Clonazepam / Q000031:analogs & derivatives* / Q000494:pharmacology; D025802:Electric Capacitance; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000648:ultrastructure; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D015398:Signal Transduction; D012964:Sodium / Q000008:administration & dosage; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000502:physiology; D013841:Thiazepines / Q000494:pharmacology; D014471:Umbilical Veins
D015220:Calcium Channels; D019831:Sodium-Calcium Exchanger; D013841:Thiazepines; D002998:Clonazepam; C079032:CGP 37157; D006632:Histamine; D012964:Sodium; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium