Effect of reduction of culture medium sodium, using different sodium chloride substitutes, on the proliferation of normal and Rous sarcoma virus-infected chicken fibroblasts.

We have substituted choline chloride, tetramethylammonium chloride, sucrose, or glucose for culture medium sodium chloride. When culture medium sodium is reduced below physiological levels (143 mM) by replacement of graded concentrations of sodium chloride with equivalent concentrations of choline chloride, normal fibroblasts approach proliferative inactivity in the presence of 90 mM Na, while their Rous sarcoma virus (RSV)-infected counterparts proliferate actively; both normal and neoplastic cells die with further sodium reduction. When culture medium NaC; is replaced with tetramethylammonium chloride, however, both normal and RSV-infected fibroblasts alike approach proliferative inactivity in the presence of 110 mM Na and both die off in the presence of 90 mM Na. When culture medium NaCl is replaced with sucrose or glucose yet another set of results is obtained: both normal and RSV-infected fibroblasts proliferate at reduced, although significant, rates in the presence of 42 mM Na. It is clear from our experimental results that the effects of reduction of culture medium sodium on cell proliferation differ markedly with the use of different sodium chloride substitutes. Caution must be exercised, therefore, in drawing inferences concerning the role of sodium in mitogenesis from experimental studies based on the tactic of reduction of external sodium.