The effect of extracellular calcium and magnesium on the proliferation of murine lymphoblasts

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Abstract
We have shown that the murine lymphoblast, L5178Y, requires extracellular magnesium or calcium for proliferation in suspension culture. Although both cations produce biphasic effects on growth, magnesium is the more potent since it: (1) stimulates proliferation at lower concentrations; (2) supports optimal proliferation over a wider concentration range; (3) maintains higher cell densities at stationary phase; and (4) produces less inhibition at high concentration.At suboptimal concentrations, calcium facilitates the effect of magnesium but at optimal concentration, no facilitation is evident. A concentration of 3.2 mM calcium or magnesium inhibits growth, while the same concentration composed of equimolar calcium and magnesium does not inhibit proliferation.Extracellular calcium and magnesium may influence proliferation by effecting changes in intracellular calcium and magnesium since: (1) reduction in extracellular concentrations sufficient to produce decreased growth rate is associated with decreased cell calcium and magnesium; (2) cell magnesium and growth rate are related such that an exponential decrease in relative doubling time occurs with decrease in cellular magnesium.Cells cultured at 37°C in magnesium and calcium‐deprived medium will proliferate at a normal rate if either or both cations are replaced within six to 10 hours; however, with longer deprivation the doubling time in restored medium is progressively lengthened.