title: 31P nuclear magnetic relaxation studies of phosphocreatine in intact muscle: determination of intracellular free magnesium.
abstract: 31P nuclear magnetic relaxation rates for phosphocreatine in intact frog gastrocnemius were compared with those observed in model solutions at 4 degrees, a temperature at which muscle maintains its physiological state for at least 5 hr. Both nuclear Overhauser effect and spin-lattice relaxation rate (1/T1) experiments indicate that dipole-dipole interactions from the dominant relaxation path for 31P in intact muscle and model solutions, independent of phosphocreatine and Mg concentrations. Spin-spin relaxation rates (1/T2) measured by modified Carr-Purcell-Melboom-Gill spin-echo experiments suggest the importance of scalar coupling modulated by chemical exchange with free Mg. From these results, we estimate the free intracellular Mg in intact muscle as 4.4 mM and demonstrate that 31P T2 experiments can be used as a tool for studying free Mg levels with minimum disturbance of the intact cell.
mesh_terms: D000818:Animals; D001001:Anura; D008274:Magnesium / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D009132:Muscles / Q000032:analysis* / Q000648:ultrastructure; D010725:Phosphocreatine / Q000032:analysis*; D013997:Time Factors
chemical_list: D010725:Phosphocreatine; D008274:Magnesium
references.citation: Am J Public Health (N Y). 1919 May;9(5):358-62
references.pmid: 18010098
references.citation: Biochim Biophys Acta. 1961 Dec 9;54:338-44
references.pmid: 14478315
references.citation: J Biol Chem. 1959 Mar;234(3):466-8
references.pmid: 13641241
references.citation: J Physiol. 1951 Jun;114(1-2):71-88
references.pmid: 14861784
references.citation: J Physiol. 1977 Jun;267(3):703-35
references.pmid: 17739
references.citation: Proc Natl Acad Sci U S A. 1977 Jan;74(1):87-91
references.pmid: 13372
references.citation: J Physiol. 1977 Apr;266(3):545-65
references.pmid: 17002
references.citation: Proc Natl Acad Sci U S A. 1977 Mar;74(3):888-91
references.pmid: 15257
references.citation: J Gen Physiol. 1977 Jan;69(1):1-16
references.pmid: 299886
references.citation: Nature. 1974 Nov 22;252(5481):285-7
references.pmid: 4431445
references.citation: Proc Natl Acad Sci U S A. 1975 Dec;72(12):4966-70
references.pmid: 1747
references.citation: J Biol Chem. 1976 May 10;251(9):2584-91
references.pmid: 4452
references.citation: Proc Natl Acad Sci U S A. 1974 Jun;71(6):2487-90
references.pmid: 4366770
references.citation: Am J Physiol. 1974 Feb;226(2):452-7
references.pmid: 4544065
references.citation: Science. 1969 Dec 5;166(3910):1297-8
references.pmid: 5350329