Matrix free Mg2+ changes with metabolic state in isolated heart mitochondria.
The concentration of free Mg2+ in the matrix of isolated heart mitochondria has been monitored by using the fluorescent probe furaptra (mag-fura-2). Beef heart mitochondria respiring in a KCl medium in the absence of external Mg2+ maintain free matrix Mg2+ near 0.50 mM. Addition of Pi under these conditions decreases free Mg2+ by 0.12-0.17 mM depending on the substrate. This decrease in free Mg2+ appears to reflect changing ligand availability in the matrix. The decrease is prevented when the Pi transporter is blocked by mersalyl. Addition of ADP to initiate state 3 respiration causes a marked increase in free matrix Mg2+ (0.1-0.2 mM) that persists as long as ATP formation is taking place; free Mg2+ then returns to the base level. This cyclic change is blocked by oligomycin and carboxyatractyloside and appears to reflect to a large extent the decrease in matrix Pi that accompanies oxidative phosphorylation. Exchange of external ADP for matrix ATP may also contribute to the increase in free matrix Mg2+. Addition of an uncoupler promotes anion efflux and increases free matrix Mg2+. Similar changes in free Mg2+ on addition of Pi, ADP, or uncoupler are seen when extramitochondrial Mg2+ is buffered from 0.5 to 2 mM, but the basal free matrix Mg2+ increases as external Mg2+ concentration increases in this range. Free matrix Mg2+ also increases when total mitochondrial Mg2+ is increased by respiration-dependent uptake in the presence of Pi. It is concluded that matrix free Mg2+ changes significantly with changing ligand availability and that such changes may contribute to the regulation of Mg2(+)-sensitive matrix enzymes and membrane transporters.
Jung
D W
DW
Department of Physiological Chemistry, Ohio State University Medical Center, Columbus 43210.
Apel
L
L
Brierley
G P
GP
D000818:Animals; D002417:Cattle; D003600:Cytosol / Q000378:metabolism; D005453:Fluorescence; D066298:In Vitro Techniques; D008024:Ligands; D008274:Magnesium / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism*; D009997:Osmotic Pressure; D010100:Oxygen / Q000378:metabolism
D008024:Ligands; D008274:Magnesium; D010100:Oxygen