Ion Homeostasis during the Growth of Human Mesenchymal Stem Cell Culture. II. Age-Related Changes in Cell K+ Content.

Ionic homeostasis of human mesenchymal stem cells (MSCs) during their long-term cultivation was studied. It was found that, at early passages (second to fourth), the intracellular K⁺ content calculated for total cellular protein was almost 40% higher than in cells of the same clone after 12–15 passages. Under the same conditions, the intracellular Na⁺ content remains practically unchanged in MSCs with age. Flow cytometry assay of MSC proliferation at various passages revealed that a decrease in the intracellular K⁺ content correlated with the cell accumulation in the G1 phase of the cell cycle and was accompanied by a slower cell division. On the basis of data on monovalent ion transport in permanent cell lines of different origin, human stem cells as well as activated human lymphocytes, the mechanism of implication of K⁺ in the cell proliferation has been discussed. It is suggested that changes in cellular K⁺ content per total cell protein accompanying triggering or inhibition of cell proliferation show the involvement of K⁺ in the cell volume regulation. The high intracellular K⁺ content is important for successful proliferation of hMSCs, and the cell K⁺ content per cell protein is an informative test for assessing the functional status of stem cells in vitro. [ABSTRACT FROM AUTHOR]