title: Potassium and sodium balance in U937 cells during apoptosis with and without cell shrinkage.
abstract: Staurosporine (STS) and etoposide (Eto) induced apoptosis of the human histiocytic lymphoma cells U937 were studied to determine the role of monovalent ions in apoptotic cell shrinkage. Cell shrinkage, defined as cell dehydration, was assayed by measurement of buoyant density of cells in continuous Percoll gradient. The K+ and Na+ content in cells of different density fractions was estimated by flame emission analysis. Apoptosis was evaluated by confocal microscopy and flow cytometry of acridine orange stained cells, by flow DNA cytometry and by effector caspase activity. Apoptosis of U937 cells induced by 1 muM STS for 4 h was found to be paralleled by an increase in buoyant density indicating cell shrinkage. An increase in density was accompanied by a decrease in K+ content (from 1.1 to 0.78 mmol/g protein), which exceeded the increase in Na+ content (from 0.30 to 0.34 mmol/g) and resulted in a significant decrease of the total K+ and Na+ content (from 1.4 to 1.1 mmol/g). In contrast to STS, 50 microM Eto for 4 h or 0.8-8 microM Eto for 18-24 h induced apoptosis without triggering cell shrinkage. During apoptosis of U937 cells induced by Eto the intracellular K(+)/Na+ ratio decreased like in the cells treated with STS, but the total K+ and Na+ content remained virtually the same due to a decrease in K+ content being nearly the same as an increase in Na+ content. Apoptotic cell dehydration correlated with the shift of the total cellular K+ and Na+ content. There was no statistically significant decrease in K+ concentration per cell water during apoptosis induced by either Eto (by 13.5%) or STS (by 8%), whereas increase in Na+ concentration per cell water was statistically significant (by 27% and 47%, respectively). The data show that apoptosis can occur without cell shrinkage-dehydration, that apoptosis with shrinkage is mostly due to a decrease in cellular K+ content, and that this decrease is not accompanied by a significant decrease of K+ concentration in cell water.
authors.affiliation: Department of Physiology, University of Tübingen, Russia.
authors.forename: Valentina
authors.initials: V
authors.lastname: Yurinskaya
authors.forename: Tatyana
authors.initials: T
authors.lastname: Goryachaya
authors.forename: Irina
authors.initials: I
authors.lastname: Guzhova
authors.forename: Alexey
authors.initials: A
authors.lastname: Moshkov
authors.forename: Yuriy
authors.initials: Y
authors.lastname: Rozanov
authors.forename: Galina
authors.initials: G
authors.lastname: Sakuta
authors.forename: Anna
authors.initials: A
authors.lastname: Shirokova
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Shumilina
authors.forename: Irina
authors.initials: I
authors.lastname: Vassilieva
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
authors.forename: Alexey
authors.initials: A
authors.lastname: Vereninov
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D020298:U937 Cells
chemical_list: D005047:Etoposide; D012964:Sodium; D019311:Staurosporine; D011188:Potassium