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. 1997 Dec;73(6):3358–3370. doi: 10.1016/S0006-3495(97)78360-7

Basal intracellular free Mg2+ concentration in smooth muscle cells of guinea pig tenia cecum: intracellular calibration of the fluorescent indicator furaptra.

M Tashiro 1, M Konishi 1
PMCID: PMC1181237  PMID: 9414246

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.

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Selected References

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