Cellular Events Involved in Dietary Sodium Deprivation Induced Inhibition of B16 Melanoma Proliferation
Dietary sodium deprivation inhibits both normal growth and solid tumor proliferation. This study proposed to ascertain the presence of circulating or cellular factors induced by dietary Na+-deprivation that might alter in vitro growth of B16 melanoma cells. Serum and melanoma cells were harvested from 24 mice who were on either a Na+-containing diet (control) or Na+-restricted diet. The cells were isolated and then propagated in tissue culture. Cytoplasmic calcium ([Ca2+]i) was measured in cultured cells by dual wavelength image fluoroscopy using the indicator fura-2. Progression through the cell cycle was measured by the fluorescence activated cell sorter using propidium iodide. Cells in culture were serum-free for 24 hours; an alteration in cytoplasmic calcium [Ca2+]i after a serum challenge was the early membrane event studied, and thymidine uptake, change in cell number, and progression through the cell cycle were the later nuclear events evaluated. A 2-way factorial analysis (diet vs. serum/cells) showed the main effect of serum from the Na+-restricted mice was a lesser rise in [Ca2+]i than from control serum (53 ± 22 vs. 111 ±29 nM/liter (mean ± SEM)). There were also differences in the cellular response from mice on different diets.