Laser flow measurements of scattering and fluorescence from cell nuclei in the presence of increasing Mg++ concentrations

Abstract

The effects of Mg++ on the spatial organization of nuclei from rat hepatocytes are analyzed in the range 0-60 mM, in the presence of suitable concentrations of KCl to reproduce physiological conditions. It is shown that the scatter-signal distribution measured by means of a flow microfluorimeter is greatly affected by this range of Mg concentrations. By coupling this result to phase-contrast-automated image analysis, it is possible to identify a shrinking process induced by Mg++ in the range 0-2.5 mM, which reaches a plateau in the range 5-20 mM and is followed by a swelling process in the range 30-60 mM. The same Mg ranges are shown to affect the intercalation of the fluorochrome acridine orange into chromatin, suggesting that the shrinking-swelling phenomenon has also a molecular correspondence at the genome level. Possible implications in terms of the influence of Mg++ on the organization of chromatin inside intact cells are briefly discussed.

Cell membrane‐dependent chromatin condensation

“…Therefore, it seemed reasonable that divaleiit cations inside the intact cells were responsible for this effect, taking into account a well-recognized role of these cations in chromatin condensation ( 1,13,29). Addition of MgCl, (as well of CaCI,) in the range of [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] mM to cell suspensions in PBS (with 0.7 mM EDTA) before treatment with detergent did result in some condensation (data not shown). However, it turned out that addition of these ions also resulted in lowering the pH by 0.2-0.3 units.…”

“…The chromatin condensation state was shown to depend on ionic properties such as ionic strength, concentration of divalent cations, pH, and type of small anion species ( 1,13,15,16,29). However, these data were obtained with the use of chromatin fragments after multistage preparation procedures and often in the range of conditions beyond those assumed to exist inside the living eukaryotic cell.…”

Effect of aniosmotic media on the volume of the T-lymphocyte nucleus

“…The volume of isolated nuclei of rat liver cells varies with Mg++ concentrations. However, this effect is only observed for divalent cations (Grattarola et al, 1985;Manning, 1978). The nucleus of intact cells, like isolated nuclei, cannot respond in an active way to variations in osmotic pressure, induced by K+ or Na+ concentration changes.…”