title: Basal intracellular free Mg2+ concentration in smooth muscle cells of guinea pig tenia cecum: intracellular calibration of the fluorescent indicator furaptra.
abstract: Longitudinal muscle strips dissected from tenia cecum of guinea pig were loaded with the Mg2+ indicator, furaptra, and the relation between the fluorescent ratio signal (R) and cytoplasmic free Mg2+ concentration ([Mg2+]i) was studied in smooth muscle cells at 25 degrees C. After the application of ionophores (4-bromo-A23187, monensin, and nigericin), a small immediate offset of R (deltaRjump) was followed by a slow change in R (deltaRslow), which reached a steady level within 2-5 h. The deltaRjump was independent of Mg2+ concentration in solution ([Mg2+]o), and was thought to be unrelated to the change in [Mg2+]i. The direction of the deltaRslow depended on [Mg2+]o with a reversal at approximately 1 mM [Mg2+]o. The intracellular calibration curve was constructed from the steady levels of deltaRslow, and the dissociation constant was 5.4 mM. With the intracellular calibration curve and correction for the deltaRjump, basal [Mg2+], was estimated to be 0.98 +/- 0.05 mM (mean +/- SE, n = 12). When the same calibration was applied to A7r5 cells and rat ventricular myocytes, estimates of basal [Mg2+]i of these cells were 0.74 +/- 0.02 mM (n = 33) and 1.13 +/- 0.06 mM (n = 9), respectively. These results suggest that the basal [Mg2+] level is approximately 1 mM at least in some types of smooth muscle cells, as generally found in striated muscles.
authors.affiliation: Department of Physiology, The Jikei University School of Medicine, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tashiro
authors.forename: M
authors.initials: M
authors.lastname: Konishi
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002432:Cecum / Q000187:drug effects / Q000378:metabolism*; D002460:Cell Line; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D007476:Ionophores; C058776:2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid; D000255:Adenosine Triphosphate; D008274:Magnesium; D016257:Fura-2