Effect of calcium on differentiation of Friend leukemia cells

Induction of hemoglobin synthesis of Friend leukemia cells is inhibited by changing the ratio between internal and external Ca²⁺ concentrations. The concentration ratio can be successfully manipulated by the addition of the growth medium of (1) Ca²⁺ channel blocker D600 (90 nM-4 × 10² nM), (2) Ca²⁺ ionophore A23187 (1 × 10²–2 × 10² nM), and (3) EGTA at molar concentrations comparable to the Ca²⁺ concentration of the medium formulation (3 × 10² μM). The observations suggest that a specific ratio between intra- and extracellular Ca²⁺ is required for erythroid differentiation to proceed.