We have used the human calcium- and temperature-dependent (HaCaT) keratinocyte cell line to elucidate mechanisms of switching from a proliferating to a differentiating state. When grown in low calcium medium (<0.1 mM) HaCaT cells proliferate. However, an increase in the calcium concentration of the culture medium, [Ca2+]0, induces growth arrest and the cells start to differentiate. Numerous studies have already shown that the increase in [Ca2+]0 results in acute and sustained increases in intracellular calcium concentration, [Ca2+]i. We find that the Ca2+-induced cell differentiation of HaCaT cells is also accompanied by a significant decrease in mitochondrial membrane potential, DeltaPsi. By combining patch-clamp electrophysiological recordings and microspectrofluorimetric measurements of DeltaPsi on single cells, we show that the increase in [Ca2+]i led to DeltaPsi depolarization. In addition, we report that tetraethylammonium (TEA), a blocker of plasma membrane K+ channels, which is known to inhibit cell proliferation, and 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), a blocker of plasma membrane Cl− channels, also affect DeltaPsi. Both these agents stimulate HaCaT cell differentiation. These data therefore strongly suggest a direct causal relationship between depolarization of DeltaPsi and the inhibition of proliferation and induction of differentiation in HaCaT keratinocytes.
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Savignan, F., Ballion, B., Odessa, M.F. et al. Mitochondrial membrane potential (DeltaPsi) and Ca2+-induced differentiation in HaCaT keratinocytes. J Biomed Sci 11, 671–682 (2004). https://doi.org/10.1007/BF02256133
- Cell differentiation
- Cell proliferation
- Ionic conductances