Intracellular ionic changes in normal and transformed human fibroblasts after extracellular Ca2+ deprivation

Area of Science:

• Cell Biology
• Biochemistry

Background:

• Extracellular calcium (Ca2+) is crucial for regulating cell cycle progression.
• Fibroblast cell lines, including normal WI38 and SV40-transformed variants, are commonly used models to study cell cycle regulation.

Purpose of the Study:

• To investigate the differential effects of extracellular calcium concentration on the cell cycle progression of normal and SV40-transformed WI38 fibroblasts.
• To elucidate the underlying ionic content and transport mechanisms responsible for these differential growth responses.

Main Methods:

• Cell culture of normal and SV40-transformed WI38 fibroblasts.
• Manipulation of extracellular Ca2+ concentration in growth media.
• Measurement of intracellular ionic content (Na+, K+, Ca2+).
• Assessment of unidirectional ion influx and active ion efflux (ouabain-sensitive).

Main Results:

• Ca2+ deprivation reversibly arrested normal WI38 cells in early G1/G0 phase, while transformed cells were unaffected.
• Normal cells showed a significant increase in intracellular Na+ content and enhanced active Na+ efflux upon Ca2+ deprivation.
• Transformed cells exhibited a substantial loss of intracellular Ca2+ (nearly 60%) compared to normal cells (10%) during Ca2+ deprivation.
• Ca2+ deprivation had minimal impact on Na+ influx and efflux in transformed cells.

Conclusions:

• Differential regulation of ion transport and membrane permeability in response to Ca2+ deprivation underlies the distinct cell cycle behavior of normal versus SV40-transformed WI38 fibroblasts.
• Altered Ca2+ homeostasis and Na+ handling in transformed cells may contribute to their resistance to Ca2+-mediated growth arrest.