Potentialization of ATRA-induced differentiation of NB4 cells by tBHQ.

(A) Ca²⁺ release from intracellular pools was measured spectrofluorimetrically in NB4 cells immediately after addition of various concentrations of tBHQ (3-40 μM). Ca²⁺ release values were compared with the maximal release obtained using 40 μM tBHQ. Sixty percent of Ca²⁺ mobilization was obtained at approximately 8 μM tBHQ. (B) Cells were treated with vehicle (lane 1), 8 μM tBHQ (lane 2), 50 nM ATRA (lane 3), 8 μM tBHQ in combination with 50 nM ATRA (lane 4), and 1 μM ATRA (lane 5); and cellular NADPH oxidase activity was determined by NBT reduction. Mean ± SEM (n = 3).