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Walker tumor cells express larger amounts of the antiapoptotic protein Bcl‐2 and presents higher resistance to toxic concentrations of Ca 2+ than the tumor cells K 562
Author(s) -
Milani Graziela,
Kowaltowski Alicia J.,
Saad Sara T.O.,
Metze Konradin,
Vercesi Anibal E.
Publication year - 2001
Publication title -
drug development research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.582
H-Index - 60
eISSN - 1098-2299
pISSN - 0272-4391
DOI - 10.1002/ddr.1154
Subject(s) - mitochondrion , digitonin , cytosol , intracellular , microbiology and biotechnology , biology , organelle , cell culture , membrane potential , transfection , inner mitochondrial membrane , biochemistry , biophysics , chemistry , membrane , enzyme , genetics
Ca 2+ homeostasis was studied in two tumor cell lines (Walker 256 and K 562) previously shown to exhibit different mitochondrial Ca 2+ accumulation capacity. When intact, both cells present cytosolic Ca 2+ concentrations within the range expected for mammalian cells, as determined through fura‐2 fluorescence ratios. In order to study intracellular Ca 2+ distribution, digitonin was used to permeabilize the plasma membrane without affecting intracellular organelle structure, as assessed using electron microscopy. Digitonin‐permeabilized Walker 256 cells incubated with Ca 2+ presented uptake of the cation exclusively through mitochondrial activity. In addition, very large Ca 2+ loads were necessary to promote a disruption of Walker 256 mitochondrial membrane potential. K 562 cells presented active Ca 2+ uptake through both nonmitochondrial and mitochondrial compartments and suffered disruption of mitochondrial membrane potential at lower Ca 2+ loads than Walker 256 mitochondria. The higher Ca 2+ resistance in Walker 256 cells could be attributed to Bcl‐2 overexpression, as evidenced by immunocytochemical staining. Thus, we correlate natural Bcl‐2 overexpression, observed in Walker 256 cells, with higher resistance to mitochondrial Ca 2+ overload, as was shown previously in mitochondria from cells transfected with the bcl‐2 gene. Drug Dev. Res. 52:508–514, 2001. © 2001 Wiley‐Liss, Inc.