title: Discrimination of intra- and extracellular 23Na+ signals in yeast cell suspensions using longitudinal magnetic resonance relaxography.
abstract: This study tested the ability of MR relaxography (MRR) to discriminate intra- (Nai+) and extracellular (Nae+)23Na+ signals using their longitudinal relaxation time constant (T1) values. Na+-loaded yeast cell (Saccharomyces cerevisiae) suspensions were investigated. Two types of compartmental 23Na+T1 differences were examined: a selective Nae+T1 decrease induced by an extracellular relaxation reagent (RRe), GdDOTP5-; and, an intrinsic T1 difference. Parallel studies using the established method of 23Na MRS with an extracellular shift reagent (SRe), TmDOTP5-, were used to validate the MRR measurements. With 12.8 mM RRe, the 23Nae+T1 was 2.4 ms and the 23Nai+T1 was 9.5 ms (9.4 T, 24 degrees C). The Na+ amounts and spontaneous efflux rate constants were found to be identical within experimental error whether measured by MRR/RRe or by MRS/SRe. Without RRe, the Na+-loaded yeast cell suspension 23Na MR signal exhibited two T1 values, 9.1 (+/-0.3) ms and 32.7 (+/-2.3) ms, assigned to 23Nai+ and 23Nae+, respectively. The Nai+ content measured was lower, 0.88 (+/-0.06); while Nae+ was higher, 1.43 (+/-0.12) compared with MRS/SRe measures on the same samples. However, the measured efflux rate constant was identical. T1 MRR potentially may be used for Nai+ determination in vivo and Na+ flux measurements; with RRe for animal studies and without RRe for humans.
authors.affiliation: Physiological NMR Core Laboratory, Division of Cardiovascular Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Yajie
authors.initials: Y
authors.lastname: Zhang
authors.forename: Marie
authors.initials: M
authors.lastname: Poirer-Quinot
authors.forename: Charles S
authors.initials: CS
authors.lastname: Springer
authors.forename: James A
authors.initials: JA
authors.lastname: Balschi
mesh_terms: D007202:Indicators and Reagents; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000378:metabolism; D012964:Sodium / Q000032:analysis* / Q000378:metabolism; D012975:Sodium Isotopes / Q000032:analysis
chemical_list: D007202:Indicators and Reagents; D012975:Sodium Isotopes; D012964:Sodium