title: Cytosolic free magnesium in stimulated, hypoxic, and underperfused rat heart.
abstract: The aim of this study was to determine whether acute changes in [Mg2+]free occur during increased hydrolysis of cytosolic ATP, and whether these changes were of sufficient magnitude to be involved in the modulation of myocardial metabolism. 31P-NMR was used to estimate free cytosolic Mg2+ levels ([Mg2+]free) during hypoxia, isoproterenol stimulation, and graded low-flow ischemia in crystalloid perfused, isovolumic rat hearts. Cytosolic [Mg2+]free was calculated to be 0.73 +/- 0.12 mM in control hearts (100 mmHg hydrostatic pressure, 95% O2, n = 18). Cytosolic [Mg2+]free increased gradually during 10 min periods of hypoxia (65%, 50%, 35%, 5% O2), and 20 min infusions of isoproterenol (0.4, 3.0, 75 nM), to maximum values greater than 250% of control (P less than 0.05). During 8 min periods of graded low-flow ischemia (12.0, 7.2, 5.3, 3.4, and 1.6 ml/min/g), [Mg2+]free did not change significantly. [Mg2+]free displayed an inverse linear correlation with total cytosolic [ATP] during isoproterenol infusion (r = 0.87), and an exponential correlation during hypoxia (r = 0.82). The data indicate that acute changes in cytosolic [Mg2+]free can occur during conditions of net ATP hydrolysis although changes in ATP alone do not appear to be solely responsible for the changes in [Mg2+]free. Since the magnitude of the changes in [Mg2+]free are sufficient to alter equilibria of enzymes such as creatine kinase and myokinase, it is possible that these changes are involved in the acute modulation of myocardial metabolism.
authors.affiliation: Chemistry and Biochemistry Department, James Cook University Townsville, Qld., Australia.
authors.forename: J P
authors.initials: JP
authors.lastname: Headrick
authors.forename: R J
authors.initials: RJ
authors.lastname: Willis
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003327:Coronary Disease / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008274:Magnesium / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D010710:Phosphates; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010710:Phosphates; D010759:Phosphorus Isotopes; D011522:Protons; D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D008274:Magnesium; D007545:Isoproterenol